http://www.legislation.gov.uk/ukpga/Vict/54-55/39/section/6Stamp Act 1891An Act to consolidate the Enactments granting and relating to the Stamp Duties upon Instruments and certain other enactments relating to Stamp Duties.texttext/xmlenStatute Law Database2020-10-05Expert Participation2020-07-22 Part I61Where an instrument is chargeable with ad valorem duty in respect ofaany money in any foreign or colonial currency, orbany stock or marketable security,the duty shall be calculated on the value, on the day of the date of the instrument, of the money in British currency according to the current rate of exchange, or of the stock or security according to the average price thereof.2Where an instrument contains a statement of current rate of exchange, or average price, as the case may require, and is stamped in accordance with that statement, it is, so far as regards the subject matter of the statement, to be deemed duly stamped, unless or until it is shown that the statement is untrue, and that the instrument is in fact insufficiently stamped.S. 6 extended by Finance Act 1985 (c. 54, SIF 114), s. 88