( 1 ) THE plaintiff Corporation of Calcutta is claiming in this suit repayment or refund of Rs. 40,871/- from the defendant, as money paid to the defendant by mistake of fact and law.

( 2 ) THE defendant carries on business as engineer and contractor. In Janu-ary/march, 1952, the plaintiff Corporation of Calcutta invited tenders for completion of Dry Water Flow Channel for 'dr. Dey's Kulti Outfall Scheme', for construction of channels. The defendant submitted tenders. Three contracts were entered into between the plaintiff and the defendant. The first contract was executed on April 29, 19. 52, the second contract was executed on April 29, 1952 and the third contract was executed on November 1, 1952. The contracts were made as per specifications and tenders of the defendant. Tenders were sent along with forwarding letters of the defendant. Each of the forwarding letters of the defendant to the plaintiff provided as follows:--"we have not provided for sales tax in our quotation. Any sales tax payable on account of this work will be to your account. "it was expressly and/or impliedly agreed by and between the parties that in case any sales tax was payable in respect of the said contracts by the defendant to the State of West Bengal, the plaintiff will reimburse the defendant for the same. In terms of the said agreement between the parties the works of construction of dry water flow channel was carried on by the defendant and completed in the year 1953. The defendant, from time to time, submitted bills to the plaintiff, for sales tax which the defendant claimed to have paid to the State of West Bengal, in respect of the said contracts. The defendant stated that the total amount so paid by the defendant was Rs. 54,498. 42 p. The particulars of the same will appear as hereunder:

Number of the Bill Date of the bill Particulars of the contract AMOUNT

H. C. O. /ob/69 K. W. B. /s. F. B. 15. 3. 54 Manufacture of bricks at Kantatola Rs. 22,229. 75 paise

H. C. O . /ob/s 23. 3. 56 Remodelling Topsia-Kulti Road . Zone IV

Rs. 3,570. 94 paise

H. C. O. /ob/1 23. 3. 56 D W F Channel 1-3 miles Rs. 15,483. 81 paise

H. C. O. /ob/2 23. 3. 56 -do- do- 4th mile Rs. 4,524. 71 paise

H. C. O. /ob/3 23. 3. 56 -do- do- 5th mile Rs. 4. 531. 73 paise

H. C. O. /ob/4 23. 3. 56 -do- do- 6th mile Rs. 4,157. 48 paise Rs. 54,498. 42 paise      

The defendant wrote to the plaintiff on January 10, 1957, demanding from the plaintiff an advance of Rs. 50,000/- against the sum of Rs. 54,498. 42 paise, which the defendant stated that they have already paid as sales tax to the State of West Bengal. On September 27, 1957, the plaintiff advanced a total sum of Rs. 40,871/- to the defendant for sales tax, relying and/or acting on the representation of the defendant. In or about April 1958, the plaintiff discovered that the said payment of Rupees 40,871/- was made by mistake of fact and law. On September 25, 1958, the plaintiff wrote to the defendant asking for refund of the amount received by the defendant from the plaintiff on account of sales tax. The plaintiff enclosed with the said letter, a copy of the report and opinion of the law officer o the plaintiff, to the effect that the contracts entered into between the parties were construction contracts and bricks manufactured on Corporation land and supplied at a cost fixed under the contracts by the contractors and the Corporation for exclusive use of the work to be done, as such there was no liability to pay sales tax on such contract in view of the decision of the Supreme Court in and also the judgment of the Calcutta High Court in. According to the plaintiff the payment of Rs. 40,871/- was made by mistake and the mistake was discovered in or about April, 1958 after the decision of the Supreme Court reported in 1958 SC page 560 (Gannon Dunkerley's case), holding, that no sales tax is payable on construction contracts as stated above, became known to the plaintiff. As