Subject to subsection (2) below, in this Part of this Act "instrument" means—
any document, whether of a formal or informal character;
any stamp issued or sold by a postal operator;
any Inland Revenue stamp; and
any disc, tape, sound track or other device on or in which information is recorded or stored by mechanical, electronic or other means.
A currency note within the meaning of Part II of this Act is not an instrument for the purposes of this Part of this Act.
A mark denoting payment of postage which the a postal operator authorises to be used instead of an adhesive stamp is to be treated for the purposes of this Part of this Act as if it were a stamp issued by the postal operator concerned.
In this section "postal operator" has the meaning given by section 27 of the Postal Services Act 2011 .
In this Part of this Act "Inland Revenue stamp" means a stamp as defined in section 27 of the Stamp Duties Management Act 1891.