The Zinoviev letter

The forgery is not seriously disputed. No original was ever produced; the document was a copy of a copy. Soviet and Comintern archives, opened after 1991, contain no trace of it in the outgoing correspondence where it would necessarily appear. The most likely production route runs through White Russian émigré circles in Riga and Berlin, which manufactured anti-Soviet documents for sale.

The operational question is the one the British government eventually answered about itself. In 1998 the Foreign Secretary asked the FCO's chief historian, Gill Bennett, to establish what had happened. Her report, published in 1999 with access to SIS and Security Service files, concluded that the letter was a forgery; that it had reached British intelligence through émigré networks; and that although no single officer could be shown to have leaked it, there were officers of SIS and MI5 with the motive, the contacts and the political sympathies to do so, and that the leak to the Daily Mail and to Conservative Central Office almost certainly came from within that world. Desmond Morton of SIS and Major Joseph Ball, later of MI5 and then the Conservative Research Department, feature in the account.

Bennett was careful about what the file could not show, and her caution is worth preserving: the identity of the forger has never been established, and the leak was proved by pattern and proximity rather than by a document naming the leaker. What is established is that the British state circulated, and gave apparent official confirmation to, a forged document four days before a general election.