Saikia, C. J. — The petitioner company impugns the Notices of Demand dated 27.4.1960 and 7.4.1975 issued by the Superintendent of Taxes, Jorhat, the farmer demanding the sum of Rs. 6,439.86 and the latter, issued after part payment, demanding the balance amount of Rs. 3,000/-payable by it for the period ending 31.12.59 as per the impugned Assessment Order dated 24.3.60 made under the Assam Taxation (on Goods carried by Road or on Inland Water-ways) Act, 1954 and prays for refund of Rs, 3439.86 p already deposited by it pursuant to the Demand Notice dated 27.4.60. The petitioner company carries -on the business of cultivation, manufacture and sale of tea in the Kamalpur Tea Estate despatching some of its products to Calcutta. 2. In 1954 the Assam Taxation (on Goods Carried by Road or on Inland Water-ways) Act, 1954 was passed levying taxes on manufactured tea carried by road or Inland water-ways. The petitioner company submitted a voluntary return for the period ending on 31.12.59, but the return was not accompanied by any receipt showing the payment of the taxes in accordance with the return and it was filed beyond 30 days prescribed under section 7(3) of that Act. The Superintendent of Taxes, Jorhat made an assessment purportedly under section 9(3) of that Act determining Rs. 6439'86 p as taxes payable and accordingly the impugned notice dated 27.4.6J was sent to the petitioner company demanding payment on or before 30.5.60; and the company deposited Rs.3439-86 p Another letter dated 11.8.1960 from the Superintendent of Taxes demanded the balance by 18.8.60. 3. Meanwhile the validity of the Act of 1954 was challanged in Civil Rule Nos. 8,9,26 and 32 of 1955 and in H. P. Baruah v. State of Assam, AIR 1955 Assam 249 the Special Bench held that Act to be valid. However, in Atiabari Tea Co. Ltd. and Khayerbari Tea Co. Ltd. v. the State of Assam AIR 1961 SC 232 , decided on 26.9.1960 it was held that the Act of 1954 was passed by the Assam Legislature under entry 56 in list 2 to collect taxes on goods solely on the ground that they were carried by road or by inland water-ways within the area of the State. Ltd. v. the State of Assam AIR 1961 SC 232 , decided on 26.9.1960 it was held that the Act of 1954 was passed by the Assam Legislature under entry 56 in list 2 to collect taxes on goods solely on the ground that they were carried by road or by inland water-ways within the area of the State. That being so, the Act had put a direct restriction on the freedom of trade, and since in doing so it had not complied with the provisions of Art. 304(b), nor had it been validated by the assent of the President under Art. 255(c), it must be declared, to be void. AIR 1955 Assam 249 was reversed. Thereafter the Assam Taxation (on Goods Carried by Road or on Inland Water-ways) Act, (Act 10 of 1961), hereinafter referred to as 'the Act of 1961', was enacted, and received the assent of the President of India on 6.4.61. It was published in the Assam Gazette Extra-ordinary dated 15th April, 1961. Section 1(3) of the Act provided that the Act of 1961 should be deemed to have had effect on or before 24th April, 1954 and should remain in force till 31.3.62. 4 After 15 years thereof the second impugned notice dated 7.4.75 was issued demanding the payment of the balance Rs. 3.000/-. This writ petition was moved on 4.7.75 and rule was issued and interim stay granted on the same day. 5. The validity of the Act of 1961 was also challenged and this Court by judgment and order dated 1.6.83 declared the Act to be ultra vires. Against that judgment and order the State of Assam and other respondents appealed before the Supreme Court. In the meantime M/s. Khayerbari Tea Co. Ltd. also challenged the provisions of the Act directly before the Supreme Court by filing an application under Article 32 and the Supreme Court in Khayerbari Tea Co v Sate of Assam, AIR 1964 SC 925 decided on 13.12.63 held the Act of 1961 to be valid. 6 Proceeding on that basis we find that under section 7(1) of the-Act of 1961-Every producer and dealer shall furnish returns of manufactured tea carried in tea containers in such from and to such rarity as may be prescribed. Under sub-sec. 6 Proceeding on that basis we find that under section 7(1) of the-Act of 1961-Every producer and dealer shall furnish returns of manufactured tea carried in tea containers in such from and to such rarity as may be prescribed. Under sub-sec. (2) of that Section of the case of any producer of dealer who, in the opinion of the Commissioner, is liable' to pay any tax for any return period or a part thereof, the Commissioner may serve, within two years of the expiry of the aforesaid period, a notice in the prescribed form upon him requiring him to furnish a return of goods carried and such producer or dealer shall thereupon furnish the return within the date and to the authority mentioned in the notice. Under sub. sec.(3) thereof the returns during the first year of operation of this Act, shall be forwarded for such period and within such time as may be notified by the Commissioner and thereafter quarterly and within thirty days of completion of the quarter in respect of which the returns are to be filed. Under sub. Sec. (1) of Section 20 of the Act tax payable under the Act shall be paid in Me manner therein­after provided. Under sub. Sec. (2) thereof, before any producer or dealer furnishes the return required by sub. Section (1) of Section 7 he shall in prescribed manner pay into the Government Treasury the full amount of tax due from him under this Act on the basis of such returns and shall furnish along with the returns on receipt for such -treasury in token of payment of such tax. 7. Admittedly, for the assessment perio4 ending 31.12.59, the return submitted by the petitioner company was voluntary and the full amount or any amount of tax due from the assessee on the basis of that return was not deposited and no treasury receipt was therefore attached. Admittedly, on notice under section 7 (2) of the Act was served on the petitioner company by the authority in respect of the assessment period ending 31 12.59. Admittedly, on notice under section 7 (2) of the Act was served on the petitioner company by the authority in respect of the assessment period ending 31 12.59. The respondents contend that as there was a voluntary return, the question of issue of notice under section 7 (2) of the Act of -1954 did not arise and that though the return was not accompanied by treasury receipt showing payment of the tax as per return it was a valid return and that the petitioner company was served notice dated 10.3.60 under section 9 (2 of the 1954 Act requiring him to produce the books of accounts in support of the return and that notice was within two years of the return period. The respondents also state that the petit­ioner company complied with that notice by producing the accounts on verification of which the impugned up assessment order dated 24.3.6C under section 9 (3) of the 1954 Act end the impugned notice of demand dated 28.4.60 were issued. Admittedly, section 33 of the Act of 1961 repealed the 1954 Act. As per provisions of section 34 of the Act of 1961 all action whatsoever taken or done under the repealed Act was validated. The respondents further state that the Act of 1961 was challenged by the petitioner company in Civil Rule No. 81 of 1961 where in that Act was declared invalid by this Court by judgment dated 1.8.63 which judgment was reversed by the Hon'ble Supreme Court by judgment dated 1.4.68 and that thereafter only the letters dated 7-4.75 and 25.4.76 were issued to the petitioner company. They contend that the assessment proceedings having been initiated within the period of limitation specified in the 1954 Act the impugned assess­ment order and the notices of demand are legal and valid and there could be no question of any refund of the amount already paid and of not paying the balance of Rs. 3,000/-. 8. The first question to be decided, therefore, is whether the return submitted without depositing the tax due was a valid return. 3,000/-. 8. The first question to be decided, therefore, is whether the return submitted without depositing the tax due was a valid return. In Bormahjan Tea Company Ltd. v. The Superintendent of Taxes, Tezpur & Ors., 1974 H.L.R. 115, it was held that a return under section 7 (1) must be submitted within the period of 30 days after completion of Return quarter, as required under s. 7 (3) of the Act, in order validly to initiate assessment proceedings based there on and Returns submitted after the statutory period must be held to be non-est. for the purpose of initiating assessment proceedings based there on. The requirement of payment of tax before furnishing a return under s. 7(1) of the Act, is a mandatory one inasmuch as a failure to do so would defeat the objects of the statute, namely, realisation of tax at the time specified in the Act and also because certain penalty is attached to such failure under s. 13 (1) (a) and (d) of the Act, On the facts of that case it was held that the (Return submitted, although within the prescribed was not a Return within the meaning of s. 7 (1) read with s. 7 (3) and s. 20 (2) of the Act, as before it was furnis­hed, the tax due on the basis of it had not been paid into a Govern- I meat Treasury, contrary to the mandatory requirement to that effect in s. 20 (2) of the Act?) On appeal therefrom the Supreme Court in Supdt, of Taxes, Tezpur and Ors. v. Bormahjan Tea Co. Ltd., (1978) I SCC 513 found that the two appeals related to assessment quarters ending on September 30, 1960 and December 31, 1960 under the Act of 1961. In one case the return was tiled within time but without payment of tax, and in the other the return was filed out of time and without payment of tax. Admittedly no notice either under section 7 (2) or section 11 of the Act was served on the respondent for the submission of the return for the periods in question. Orders of assessment were, however, passed in both the cases in June 1969 in pursuance of the provisions of Section 9 (4) of the Act. Admittedly no notice either under section 7 (2) or section 11 of the Act was served on the respondent for the submission of the return for the periods in question. Orders of assessment were, however, passed in both the cases in June 1969 in pursuance of the provisions of Section 9 (4) of the Act. The orders of assessment were challenged and the High Court held that as under section 7 (1) the return must be submitted within a period of JO days and the payment of tax was mandatory, the two. returns were non-est and as admittedly no proceedings were taken under section 7 (2) the assessment proceedings could, therefore, not be initiated based on such non-existent returns and the tax authorities were not competent to proceed with the assessment. In appeal therefrom to the Supreme Court it was contended by the appellant that me assesses could not take advantage of his omissions to pay the tax and that it was not necessary that the tax should also have been paid before a valid return was submitted and hence the returns could be treated as valid returns and assessment proceedings could be proceeded with on the returns submitted. Rejecting tae contentions and dismissing the appeal the Supreme Court held in Supdt, of Taxes, Dhubri v. Onkarmal Nathmal Trust, (1976) i SCC 766, 776 that before proceedings could be taken under section 9 (4) it is mandatory that notice under section 7 (2) will have to be issued. Therfore, the appellant-State was forced to contend that the returns filed by the respondent were not non-est and the assessment proceedings were valid. But in appeals under Article 136 of the Constitution the Supreme Court is not justified in permitting the State to contend that it can proceed on the basis that the returns were valid, especially when, before the High Court, the appellant's contention was that the returns were invalid. The power under Article 136 is discretionary and even though there may be substance in the argument put forward on behalf of appellant, the Supreme Court taking the totality of the circumstances is justified in declining to interfere in an appeal by special leave. Thus the contention that the returns are non-est was not decided though the Court observed that the contention was not without substance. The decision of the High Court that such a return was non-est was not disturbed. Thus the contention that the returns are non-est was not decided though the Court observed that the contention was not without substance. The decision of the High Court that such a return was non-est was not disturbed. In the instant case it has been contended by the petitioner company that the return was non-est. We find force in the contention. 9. Next arises the question of refund of the amount already deposited. The petitioner's contention is that the voluntary return filed- by it having been non-est the amount already deposited pursuant to the demand notice based on the assessment order on the voluntary return is to be refunded as the State had no authority to make any assessment on that return. The respondents sought to refute it submitting that the liability to pay tax under the Act was very much there and the assessment order though not validly made, that order having now been validated by the Act of 1961 the question of refund would not arise. We are referred to the Special Bench decision in Salona Tea Company Ltd, V. Superintendent of Taxes, Nowgong and Ors., Civil Rule Nos. 509 to 512 of 1973 decided on 14th June, 1979. Those petitions were directed against orders of assessment made and demand notices issued under the Act of 1961 to declare the assessment and demands as illegal and to direct the respondents to refund the tax collected pursuant of those orders. After holding that the assessment made was without jurisdiction the question whether the Court should direct refund of the amount was gone into. In this regard the distinction between those cases where a petitioner approached a High Court seeking relief of obtaining refund only; and those where refund was sought as a consequential relief after striking down of the orders of assessment etc. was considered. In this regard the distinction between those cases where a petitioner approached a High Court seeking relief of obtaining refund only; and those where refund was sought as a consequential relief after striking down of the orders of assessment etc. was considered. In so far as the first type of cases was concerned, reference was made to Suganmal v. State of Madhya Pradesh, AIR 1965 SC 1740 wherein it was not considered proper to extend the principle justifying consequential order directing the refund of amounts illegally realised when the order under which the amount had been collected, had been set aside, to the cases in which only orders for refund of money were sought and that when the claim for refund could not be brought within any statute or statutory rule, no legal duty was cast on the State to refund the amount it had realised, because the right to claim refund was not founded on any statutory law. However, in the instant case section 23 of the Act of 1961 deals with refunds and the prayer for refund cannot, therefore be said to be without any statutory basis. It is also to be noted that the petitioner has not come asking for the sole relief of refund he having also prayed for declaration that the assessment order was illegal. When aggrieved persons not only pray for striking down the order of assessment and consequential refund of the amount already paid the High Court has jurisdiction to order refund. In State of M. P. V, Bhailal Bhair AIR 1964 SC 1006 it was held that it would hardly be reasonable to say that while the Court will grant relief by making an order in the nature of injunction where the invassion of a right has been merely threatened, the Court must still refuse when the right had been actually invaded to give the consequential relief and content itself with merely a declaration that the right exists and it was invaded or with merely quashing the illegal order made. This was approved in State of Kerala V. Aluminum Industries Ltd., 16 STC 689, wherein it was further observed that where a tax was levied by mistake of law, it was ordinarily the duty of the State to refund the tax. In Tilokchand JMotichand V. H. B. Munshi, AIR 1970 SC 898 relief was refused the payment having . This was approved in State of Kerala V. Aluminum Industries Ltd., 16 STC 689, wherein it was further observed that where a tax was levied by mistake of law, it was ordinarily the duty of the State to refund the tax. In Tilokchand JMotichand V. H. B. Munshi, AIR 1970 SC 898 relief was refused the payment having . not been regarded as to have been made under mistake of law. Relief was also refused in Cawasji and Co. V. State of Mysore, AIR 1975 SC 813 . 10. Section 23 of the Act of 1961 provides : "23. Refunds. The Commissioner shall, in the prescribed manner refund to a producer or a dealer any sum paid or realised in excess of the sum due from him under this Act either by cash payment or, at the option of the producer or dealer, by set off against the sum due from him in respect of any other period. Any penalty remitted by the Commissioner shall be refunded or adjusted in the like manner." This section speaks of any sum paid or realised in excess of the sum due from the assessee. Excess means that which exceeds ; the degree or amount by which one thing exceeds another. When the due tax is paid with something which exceeds it, the excess is to be refunded under S. 23 of the 1961 Act. But will it make any difference when no tax is payable but some has been paid ? In our view this should not make any difference. The reason behind providing for, refund of the excess is that the. State should not be allowed to ( retain what is not due to it?) This will cover (any amount paid as tax when no tax is payable?) We accordingly hold that under fins provision the amount of Rs. 3,439-86 p. paid by the petitioner company would be refundable. 11. Again, a decision of this question has to be based on an accepted principle of law. When tax is paid in accordance with an assessment order made under a statute and the order is set aside and no further assessment can be made under the law the fiction of quasi contract may be applied. 11. Again, a decision of this question has to be based on an accepted principle of law. When tax is paid in accordance with an assessment order made under a statute and the order is set aside and no further assessment can be made under the law the fiction of quasi contract may be applied. Toe fiction of quasi contract was useful historically in creating a remedy for certain cases of unjust enrichment, but Lord Wright considers that the time has come at which the fiction should be abolished and the law placed on the firm ground of reasonable principle of unjust enrichment. "The fiction is the algebra of Jaw and a. picturesque form of algebra besides 12. Quasi contract means that a man in certain cases in bound as if he had made a contract, though in fact no contrail was made, "Unjust enrichment” or “restitution" are suggested as a alternative expressions. 13. The doctrine of unjust enrichment is founded on a broad principle that unjust enrichment should not be retained at the expense of one who has suffered. In French law the principle is known as 'actio de in rem verso' which is founded on the principle of equity which forbids one man to enrich himself at the expense of another. It applies in every case in which, the estate of one person being enriched without lawful cause at the expense of another person the latter in order to obtain what is due to him, does not enjoy the benefit of any action based on contract, quasi-contract, delict or quasi delict. The Polish Code (Art.123); C.C. of Japan (Art 703), Soviet Russia (Art 399-402), Chinese Code (An 179) and the Swiss Federal Code of Obligation (Art. 62) contain a general principle providing that unjust benefit must be returned. 14. The same-principle has been often discussed under the subject 'restitution'. Where a person holding title to property is under an equitable duty to convey it to another on the ground that he would be unjustly enriched if he were permitted to retain it. Lord Wright is of the view that the basis of the law should be restitution where it is unreasonable and unjust for the defendant to retain the benefit which he has received. However, the theory of implied contract still persists in law. 15. Lord Wright is of the view that the basis of the law should be restitution where it is unreasonable and unjust for the defendant to retain the benefit which he has received. However, the theory of implied contract still persists in law. 15. Restitution is the writ by which a defendant successful in an appeal, is restored to all he has lost by the execution of the judgment which is reversed; the writ by which stolen goods were formerly restored to their true owner. Restitution means the restoring of anything unlawfully taken from another It is most frequent y used in the common law for the setting them in possession of lands and tenements that has been unlawfully diseased of them. / 16. Article 265 of the Constitution of India provides that no tax shall be levied or collected except by authority of law. Where an executive authority has been empowered to collect a tax by an invalid law or rules made thereunder the Court is entitled to interfere. Acquiescence cannot take away from a party the relief he is entitled to in case of contravention of Art. 265. This Article embodies the principle of no taxation without representation.' 'Authority of law' refers to a valid law, which means that the Legislature making the law must have empetent, at the time when the taxing law was validly anacted (Ghulam v. State of Rajasthan, AIR 1963 SC 479 (484) ; Bhart Kala Bhandar v. Dhamangaon Municipality AIR 1966 SC 249 (262) , State of Mysore v. I Cowasji (1970) 3 SCC 710 (715), 'Rex hoc solum non potest fucere quod non potest injuste agere.' The King can do everything but an injustice. It will be unjust to allow the tax collected by an invalid law/' to be retained by the State/) 17. Under section 72 of the Indian Contract Act, a person to whom money has been paid, or anything delivered, by mistake or under coercion, must repay or return it. When a railway refuses to deliver up certain goods to the consignee, except upon the payment of an illegal charge for carriage and the consignee pays the sum charged in order to obtain the goods, he is entitled to recover so much of the charge as was illegally excessive. There is no question of coercion in case of payment of a tax. There is no question of coercion in case of payment of a tax. But the onerous consequences of non-payment are always " there. So the same principle of refund should apply. 18. Section 72 of the Contract Act includes payment made under a mistake of law in case of payment of a tax which is ultravires or un-u constitutional, the party is . entitled to have a refund of it from the v! Government, whether lie had paid it under protect or not)as was held in S.T.O.V. Kanhaiya Lal, AIR 1959 SC 135 . Orient Paper Mills v. State of Orissa, AIR 1961 SC 964 settled the proposition that a dire­ction for refund may be made in a proceeding for mandamus under Art. 226 of the Constitution. The prayer for refund cannot be held to be time-barred inasmuch as we have held the assessment to be ultra-vires only today. The question of having acquiesced for a long time does not arise as the assessment order was purportedly made a statute. 19. A question may arise as to whether the refund should- have been claimed by the petitioner company within three years of the Act having been declared ultra-vires on 26.9.60. But the Act of 1961 received the asseent of the President of India on 6,4.61 and it provided that the Act should be deemed to have had affect on nr before 24th April, 1954 and should remain in force till 31.3.62. The assessment was for the period ending 31.12.59. Until the assessment order was set aside the period of limitation could not run and hence the question of refund being barred by limitation does not arise in this case. 20. In the result, the impugned assessment order and the notices of demand are set aside. The respondents are directed to refund the amount of Rs. 3,439.86 P. only which was deposited by the petitioner company in response to the impugned notice dated 27.4.60., The petition is allowed and the rule made absolute. We, however, leave the parties to bear their own costs. Chief Justice Judge