http://www.legislation.gov.uk/ukpga/Vict/54-55/39/section/15Stamp 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 I151An unstamped or insufficiently stamped instrument may be stamped after being executed on payment of the unpaid duty and any interest or penalty payable.2Any interest or penalty payable on stamping shall be denoted on the instrument by a particular stamp.Ss. 15, 15A and 15B substituted (27.7.1999 with effect as mentioned in s. 109(4) of the amending Act) for s. 15 by 1999 c. 16, ss. 109(1)(4), 122, 123(4)S. 15 applied (with modifications) (retrospective to 28.3.2000 and with effect as mentioned in s. 116(2) of the amending Act) by 2000 c. 17, s. 116(2)(3), Sch. 32 para. 7