JUDGMENT 1. THE petitioner company carries on business as Engineers and Contractors and is registered as a dealer under the Bengal Finance (Sales Tax) Act, 1941 (hereinafter referred to as the Act). Between January and March, 1952 the respondent No. 5, the Corporation of Calcutta invited tenders for completion of Dry Water Flow Channel for "dr. Dey's Kulti Outfall Scheme" for construction of channel. The petitioner is stated to have entered into such contracts with the Corporation of Calcutta. Specimen copy of such tender has been annexed being Annexure 'a' to the petition. From the said tender it appears that the petitioner has to carry out and complete the whole of the works in accordance with the specifications and the terms of the agreement. It is stated that all such contracts including manufacture of bricks were works contracts and were executed in 1953. In terms of the letter dated 24.7.1971 being annexure 'b' to the petition it was agreed that if any sales tax is payable on the transactions involved in the execution of the said contracts, such sales-tax is to be realised from the, Corporation of Calcutta separately. It appears that by a letter dated 22nd September, 1953 the Commissioner of Commercial Taxes wrote to the Commissioner of Calcutta Corporation that the petitioner being a dealer registered under the Act is liable to pay tax to the government on the sale price of the contracts executed by it in favour of the corporation of Calcutta. 2. THE petitioner filed its returns as a dealer and assessments were made and a sum of Rs. 53,045.10 was determined to be the sales tax in respect of the transactions involved in the execution of the contracts with the respondent No. 5. The said sum represented the sales tax for the years 1951-52 to 1954-55. The petitioner deposited the said amount with the Reserve Bank of India. In terms of the agreement between the petitioner and the respondent no. 5, the petitioner realised a sum of Rs.40,871/- from the said respondent no. 5 by way of reimbursement of the taxes paid by it. The respondent No. 5, thereafter filed a suit against the petitioner in this Court for refund of the said sum of Rs.40,871/ - on the ground that sales tax was not payable by the said respondent No. 5 in respect of contract of Dry Water Flow Channel. 5 by way of reimbursement of the taxes paid by it. The respondent No. 5, thereafter filed a suit against the petitioner in this Court for refund of the said sum of Rs.40,871/ - on the ground that sales tax was not payable by the said respondent No. 5 in respect of contract of Dry Water Flow Channel. The said suit being suit No. 1618 of 1960 came up for hearing before Hazra, J. By a judgment delivered on 1st March, 1972, the said suit was decreed and the petitioner was directed to pay the sum of Rs. 40,871 - along with the interest thereupon at the rate of 6% per annum. His Lordship interpreting the agreements in question with the Corporation of Calcutta held them as contracts for construction and that manufacture of bricks were made for the use of the construction work and the using of bricks was part of construction contracts. Proceeding on that view it was held in that case that the principles laid down by the supreme Court in the case of (5) State of Madras v. Gannon Dunicerley and Co. (A.I.R. (1958) S.C. 560) and (1) Dakhneswar Sarkar and Bros. Ltd. v. Commercial Tax Officer and ors. (A.I.R. 1957 Calcutta 283) were attracted and no sales tax was payable on the said contracts. It has been further held that materials used for construction contracts could not be separately assessed for payment of sales tax. The learned Judge further held that when payment was made by the Corporation of Calcutta on 27th September, 1957 to the petitioner the payment was made under mistake of law and fact and hence the petitioner was directed to refund the amount of rs. 40, 8711 to the Corporation of Calcutta. The said judgment as already stated was delivered on 1st March, 1972. The petitioner thereafter moved this court under Article 226 of the Constitution for quashing assessment orders dated 29th March, 1956 and 7th August, 1959 being annexure E to the petition and for refund of the sum of Rs.53,045.10 collected from it by virtue of the assessment orders for years 1951-52 to 1954-55. On these allegations a rule nisi was issued on 8th June, 1972. 3. On these allegations a rule nisi was issued on 8th June, 1972. 3. THE learned Counsel for the petitioner contends that the contract for completion of Dry Water Flow Channels entered into with the Respondent No. 5 is a contract for the execution of works not involving sale of goods. As a result of the judgment delivered by hazra, J. on 1st March, 1972, the petitioner has discovered the mistake under which it had paid to the taxing authority's sales tax in respect of those works contracts and as the petition has been moved immediately there after, the said assessments are liable to be quashed and the amount of tax paid in respect of those contracts are liable to be refunded to the petitioner. Counsel for the respondents did not seriously contend that the contracts in question were not works contracts. He however contended that the assessments were made on the understanding of the law as it prevailed at the relevant time. If thereafter the Supreme Court gives a different interpretation of the law, the assessment remain valid assessments and until the remedies are resorted to under the Act for setting aside those assessments, there cannot be any claim for refund. It has been further contended that in any event the: judgment in the case of (5) State of madras v. Gannon Dunkerley and Co., (supra) was delivered on 1st April, 1958 the petitioner in the present case has moved this application on 8th June, 1972 claiming refund of the amount paid on the basis of assessments made on 29.3.1955 and on 17.8.1959. In such a case the claim for refund being barred under the law of limitation, cannot be allowed by a writ of mandamus. 4. TO examine the rival contentions of the parties, the circumstances under which the present petition has been filed have to be considered. Until the judgment was delivered on 1st March, 1972 by Hazra, J. in Title Suit No. 1618 of 1960 the petitioner was contending in the said suit that the sales tax has been lawfully paid on such contracts and that in terms of the agreement between the petitioner and the respondent No. 5, it has to be reimbursed in respect of the amount of sales tax paid to the taxing authorities. As a result of the decision of Hazra, J, it has been now held that the contracts in question were contracts for construction and the principles of the decision of the Supreme Court in the case of (5) State of Madras v. Gannon Dunkerley and Co. (supra) would apply to such contracts which are to be treated as indivisible works contracts and hence do not attract any sales tax as there is no sale of materials as such involved in the execution of such contracts. The petitioner specifically pleaded that the mistake of law as to the nature of transaction and the liability to pay sales tax on such transactions was discovered by it as a result of the decision of Hazra, J. in the aforesaid case. The said allegation however has been denied by the respondent Nos. 1 to 4 in the affidavit of Bani Lal Ganguly. It is true that in title Suit No. 1618 of 1960 the respondent Nos. 1 to 4 were not parties and the judgment delivered in that case may not be binding upon those respondents in this petition. The said judgment has been relied upon by the petitioner not because it is binding upon respondents Nos. 1 to 4 but in support of the contention that the mistake of law under which the sales tax has been paid was discovered as a result of the said decision. There is not dispute that the contracts entered into between the petitioner and the respondent No. 5 were for completion of Dry Water Flow Channel. There is also no dispute that the specimen, copy of the tender annexed to the petition being annexure 'a' is the type of agreement governing all the contracts with the respondent No. 5 in respect of those transactions. 5. IT is now well settled that under section 72 of the Indian Contract Act, 1872, a party is entitled to recover money paid by mistake or under coercion, and if it is established that the payment, even though it be of a tax, has been, made by the party laboring under a mistake of law, the party receiving the money is bound to repay or return it though it might have been paid voluntarily, subject however to question of estoppel, waiver, limitation or the like. (3) Sates Tax Officer, Beneras v. Kanhaiya Lal Mukund Lal Saraf and ors. (3) Sates Tax Officer, Beneras v. Kanhaiya Lal Mukund Lal Saraf and ors. (9 S.T.C. 747) S. C. The term 'mistake' appearing in Section 72 of the Indian contract Act is wide enough to comprise within its scope a mistake of law as well as a mistake of fact. The only two circumstances that entitles a party to recover the money back are that the money must have been paid by mistake or coercion. When an assessment has been made under a provision of the statute which is subsequently declared ultra vires a payment made on the basis of such an assessment can be treated as one made under a mistake of law. There is hardly any difference between such a case and one where there is no provision or authority for an assessment to be made. In both the cases the provision to levy assessment is honest. 6. WHERE a particular Act contains no machinery for refund of tax collected in excess of constitutional limit or illegally collected a suit lies. It is now well settled that challenge to the provision of a particular Act as ultra vires cannot be brought before a Tribunal constituted under that Act. Such a challenge can be made either by way of a suit or by invoking the writ jurisdiction. The normal remedy for recovery of money paid. to the State under coercion or mistake of law is by suit. Articles 32 and 226 of the Constitution provide concurrent remedy in respect of the same claim. 11 is true that the Indian Limitation Act does not directly apply to a petition under Article 226 of the Constitution, but the extraordinary remedies under the Constitution are not intended to enable the claimant to recover moneys, the recovery of which by suit is barred by limitation. Where the remedy in a writ application under Article 226 of the constitution corresponds to a remedy in an ordinary suit and the latter remedy is subject to the bar of a statute of limitation, the court in its writ jurisdiction acts by analogy to the statute, adopts the statute as its own rules of procedure and in the absence of special circumstances imposes the same limitation on the summary remedy in the writ jurisdiction. (8) Tilofo Chand Moti Chand v. H. Munshi, 25 S.T.C. 289 (S.C.). (8) Tilofo Chand Moti Chand v. H. Munshi, 25 S.T.C. 289 (S.C.). On similar ground the Court of Chancery acts on the analogy of the law of limitation applicable to action at law and frequently put a special limitation of their own if they thought that the suit was unduly delayed. This principle also Is well recognised in American practice which is outlined in corpus juris secundum. It is now well settled that the high Courts have the power for the purpose of enforcement of fundamental rights and statutory rights to give consequential reliefs by ordering repayment of money realised by the Government without the authority of law. When a provision is declared unconstitutional or an assessment has been made although there is no such authority or provision for it, the assessment is non est in the eye of law and a Writ of Certiorari may include a direction for refund if the claim is clearly within the time prescribed by the Limitation Act although it may not be a compulsory remedy to replace a suit. The special remedy provided in article 226 of the Constitution is, however, not intended to supersede completely the modes of obtaining relief by an action in a civil Court or to deny defences legitimately open in such action the power to give relief under Article 226 is a discretionary power and it is specially so in the case of power to issue Writ in the nature of Mandamus. Among several matters which the High court in the exercise of such discretion has to take into consideration is the delay made by the aggrieved party in seeking the special remedy and also the nature of controversy of facts or law to be decided as regards the availability of consequential relief. Whether repayment should be ordered in the exercise of this discretionary power will depend in each case on its own facts and circumstances. It is neither desirable nor feasible to lay down any abstract rule or formula for universal application. It may, however, be stated as a general rule that if there has been unreasonable delay the Court ought to not ordinarily lend its aids to a party by this extraordinary remedy of Mandamus. It is neither desirable nor feasible to lay down any abstract rule or formula for universal application. It may, however, be stated as a general rule that if there has been unreasonable delay the Court ought to not ordinarily lend its aids to a party by this extraordinary remedy of Mandamus. Again where even if there is no such delay the Government or the statutory authority against which the consequential relief is prayed for raises a prima facie triable issue as regard the availability of such relief on the ground like limitation the Court should ordinarily refuse to issue the Writ of Mandamus for such payment. In both these kinds of cases the parties should be left to seek their remedy by the ordinary modes of action in a Civil Court and it will be a soured use of discretion to refuse to exercise the extraordinary remedy under Article 226 of the Constitution. (4) State of Madhya Pradesh v. Bhairol, 15 S.T.C. 450 (S. C.). 7. THE period of limitation prescribed for recovery of money paid by mistake under the Limitation Act is three years from the date when the mistake is known. Although the provisions of the limitation Act do not as such apply while considering the relief to be granted under Article 226 of the Constitution the maximum period fixed by the Legislature as the time within which the relief by a suit in a Civil Court must be brought may ordinarily betaken to be a reasonable standard by which delay in seeking remedy under Article 226 of the Constitution can be measured (State of Madhya Pradesh v. Bhailal Bhai 22 S.T.C. 416 (S.C.)). The Court may, however, consider the delay as unreasonable even if it is less than the period of limitation prescribed for a civil action for the remedy, but where the delay is more than this period, it will almost always be proper for the Court to hold that it is unreasonable. 8. The Court may, however, consider the delay as unreasonable even if it is less than the period of limitation prescribed for a civil action for the remedy, but where the delay is more than this period, it will almost always be proper for the Court to hold that it is unreasonable. 8. IN the light of the principles discussed above, in my view, in such a petition asking for refund of the money on the ground that the tax has been paid under a mistake of law, it is necessary to examine (a) whether tax has been paid under a mistake of law, (b) when such mistake came to the knowledge of the petitioner and (c) whether there has been any unreasonable delay in asking for such a relief. In the case of (2) Gill and Co. Private Ltd. v. Commercial Tax officer, Hyderabad III, and anr. 22 S.T.C. 524 the High Court did not admit the writ petition on the ground that the petition for the grant of the extraordinary remedy could not be admitted after the lapse of a long period, and that the question of time when the mistake was discovered was a question of fact which had to be enquired into and the remedy by way of a suit in a court of law was a more convenient and effective remedy. The Supreme Court allowed the appeal against the order rejecting the writ petition and held that the High Court had to examine after the affidavit had been filed the question as to whether the appellant had paid the tax under a mistake of law as also when the appellant came to discover its mistake, In view of the above decision i have to examine whether the tax had been paid under a mistake of law and when the petitioner came to discover its mistake. The specimen copy of the tender being annexure 'a' to the petition shows that the petitioner has to execute and complete the construction of Dry water Flow Channel in a substantial and workmen like manner in accordance with the specification to the satisfaction of the chief Engineer and any other officer representing him. (Clause 11 of the tender). The specimen copy of the tender being annexure 'a' to the petition shows that the petitioner has to execute and complete the construction of Dry water Flow Channel in a substantial and workmen like manner in accordance with the specification to the satisfaction of the chief Engineer and any other officer representing him. (Clause 11 of the tender). Payment to the contract will be made from time to time during the course of the work at the rate of 90% upon the value of the work actually executed as certified by the Engineer. The remaining 10% shall be retained by the corporation of Calcutta till after the completion of the work when 1 1/2% of the money so retained will be paid along with the final bill for the work. (Clause19) All materials other than those supplied by the Corporation of Calcutta required for the work shall be supplied by the contractor and should be of the best quality and be approved by the chief Engineer or his representative. (Clause 12). On an examination of the relevant clauses of the specimen copy of the tender, I am of the view that the petitioner had offered to execute and complete the "work" according to the specifications and conditions and the contract was for work, and rot a contract for sale of the materials or goods as such. It is now well settled since the decision of the (1) State of Madras v Gannon Dunkerly and Co. (supra) that In a works contract there is no sale or materials as defined in the Sales of goods Act. The principle decided in the case of a building contract has been applied by the Supreme Court in other types of works contracts also (7) Stats of Rajasthan and anr. v. Man Industrial corporation Ltd. 24 S. T. C. 349 (S. C.) and (6) State of Madrcfis v. Richardson Cruders. Ltd. 21, S. T. C. 245 (S. C.)The principle as stated in Halsbury's Law of England, Vol. 34, page 6, paragraph 3 is thus "a contract for sale of goods must be distinct from a contract for words and labour. The distinction is often a fine one. Ltd. 21, S. T. C. 245 (S. C.)The principle as stated in Halsbury's Law of England, Vol. 34, page 6, paragraph 3 is thus "a contract for sale of goods must be distinct from a contract for words and labour. The distinction is often a fine one. A contract of sale is a contract whose main object is the transfer of the property in, and the delivery of the possession of, a chattel as a chattle to the buyer: Where the main object of the work under taken by the payee of the price is not the transfer of a chattel qua chattel contract is one for work and labour. The 'test' whether or not the work and labour bestowed and in anything that can properly become the subject of sale neither the ownership of the materials, nor the value of the skill and labour as compared with the value of the materials is conclusive, although such matter may be taken into consideration in determining, in the circumstances of a particular case whether the contract is in substance one for work and labour or one for the sale of a chattel. " Applying this test the contract in question, in my view, was one for work and labour and there was no contract for the sale of goods as such. In these circumstances the assessing authorities had no jurisdiction to treat such transaction as one of sale of goods. It is not within the competence of the State Legislature to impose a tax on the supply of the materials used in the execution of a works contract treating it as sale, In an appropriate case it may so happen that the parties to the contract may enter into distinct and separate contract, one for the transfer of materials for money consideration and the other for the payment of remuneration for services and for work done. In such a case there are really two agreements though there is a single instrument embodying them, and the power of the State to separate the agreement to sell from the agreement to do work and, to render services and to impose a tax thereupon cannot be questioned. (State of Madras v. Gannon Dunkerley and Co. (supra). In such a case there are really two agreements though there is a single instrument embodying them, and the power of the State to separate the agreement to sell from the agreement to do work and, to render services and to impose a tax thereupon cannot be questioned. (State of Madras v. Gannon Dunkerley and Co. (supra). Reading the agreement in my view there are no distinct and separate contract, one for the transfer of materials for money consideration and the: other for the payment of remuneration for services and for work done. It is one and indivisible contract and the; payment also is to be made on the value of the work actually executed. In these circumstances the respondents could not treat the supply of the materials involved in the execution of such contract as a sale and impose tax thereupon. 9. THE next enquiry will be when the mistake was discovered by the petitioner. It appears that in the suit filed before this court the petitioner was contesting the stand taken by the Corporation of Calcutta that no sales tax is payable on such works contract. It is as a result of the judgment delivered by hazra, J. on 1st March, 1972 in that suit that the petitioner came to know the real nature of the transaction. This application having been moved on 8th June, 1972, it cannot be said that there has been any unreasonable delay in invoking the extraordinary jurisdiction. Under Art. 226 of the Constitution. The learned Counsel for the respondents contends that the judgment in (1) Slats of Madras v. Gannon Dunkerley and Co. (supra) was delivered on 1st April, 1958 and the petitioner had not explained why this petition was not moved within three years from the date of the said decision. The petitioner till the judgment of Hazra, J. in the suit referred to above was under the impression that this transaction attracts sales tax. The mistake was discovered only as a result of the decision of this court by which the petitioner was directed to refund the amount of Rs. 40,871/- to respondent No. 5 being the sum paid to the sales tax authorities in respect of the transaction in question. The mistake was discovered only as a result of the decision of this court by which the petitioner was directed to refund the amount of Rs. 40,871/- to respondent No. 5 being the sum paid to the sales tax authorities in respect of the transaction in question. Excepting a mere safe denial the respondent No. 1 has not stated any circumstances to show that the mistake under which the taxes were paid was known to the petitioner earlier than 1.3.1972. In these circumstances I am satisfied that the mistake was discovered only on 1.3.1972 as result of the decision of Hazra, J. in the case mentioned above. It is true that the said decision is not binding upon the respondent Nos. 1 to 4 as (hey were not parties to the said suit. But the question is not whether the said decision is binding upon the respondent Nos. 1 to 4 but whether the said decision can be relied upon by the petitioner in support of the it plea that the mistake was discovered only when the said judgment was delivered. In my view the petitioner is justified in relying upon the said decision in support of its contention that the mistake was discovered only when the said judgment was delivered holding the said contract to be works contract. On an examination of both the points on the basis of the affidavit filed in this petition I am of the view that the petitioner had paid the tax under a mistake of law and that it came to discover the mistake only on 1.3.1972 and there was no unreasonable delay in asking for the relief under Art.226 of the Constitution. 10. THE result is that this application succeeds. The assessment orders dated 29.3.1955 and 17.8.1959 being Annexure e to the petition in so far as they purport to impose, sales tax for the execution of the contract for Dry Water Flow channel with the Corporation of Calcutta are quashed by, a writ of certiorari. The respondent No. 1, 2 and 4 are directed by a writ of mandamus to refund the sum collected from the petitioner by way of sales tax in respect of the said contract. As no relief has been asked for against the respondent No. 5 there will be no order against the respondent no. 5. The rule is made absolute to the extent indicated above. As no relief has been asked for against the respondent No. 5 there will be no order against the respondent no. 5. The rule is made absolute to the extent indicated above. There will be no order as to costs. Rule made absolute.