Zhdanov on the Zinoviev letter

Recently I read Jukka Nevakivi's very entertaining book Ždanov Suomessa ("Zhdanov in Finland") about Andrei Zhdanov's time as the head of the Allied Control Commission in Finland. Nevakivi describes a discussion on January 23rd, 1945, in which Zhdanov instructed Finnish Communists in the art of election propaganda. One of the examples he used was the Zinoviev letter. The interesting thing is that according to Zhdanov, the letter was of Soviet origin, but intended by them to hurt Labour. Nevakivi quotes Zhdanov thusly (my translation): "Before the election we published the forged 'Zinoviev letter' and because of this forgery, Labourites lost a part of their votes to the Conservatives..."

I haven't seen this theory in British sources. The general opinion seems to be the one from the linked article: that a few British intelligence agency officers were behind the letter's release, but that its forger is unknown. In theory Zhdanov's claim remains a possibility. On the other hand, in late 1924, when the letter was published in the Daily Mail, Zhdanov was a local official in Nizhni-Novgorod, so presumably whatever he knew about the topic he heard second hand, after the fact. The claim that the Soviets published the letter is questionable, as we know that it got to the British press from British intelligence, but it can be interpreted loosely, I suppose.