Frederick Forsyth: The Fourth Protocol (used)

The Fourth Protocol is a thriller novel by British writer Frederick Forsyth and published in August 1984.

On New Year's Eve 1986, professional thief James Rawlings breaks into the apartment of a senior civil servant and inadvertently discovers stolen top secret documents. Despite being a notorious and infamous criminal, he is enough of a patriot to send the documents anonymously to MI5 so that they might locate the traitor. In Moscow, British defector Kim Philby drafts a memorandum for the Soviet General Secretary stating that, should the Labour Party win the next general election in the United Kingdom (scheduled for sometime in the subsequent eighteen months), the "hard left" of the party will oust the moderate populist Neil Kinnock in favour of a radical new leader who will adopt a true Marxist-Leninist manifesto, including the expulsion of all American forces from the United Kingdom and the country's withdrawal from (and repudiation of) NATO. In conjunction with a GRU general, an academic named Krilov, and a master strategist, they devise "Plan Aurora" to secure a Labour victory by exploiting the party's support for unilateral disarmament.

John Preston, an ex-Parachute Regiment soldier-turned-MI5 officer, who was exploring hard-left infiltration of the Labour Party, is tasked to investigate the stolen documents and discovers they were leaked by George Berenson, a passionate anti-communist and staunch supporter of apartheid South Africa. Berenson passed on the documents to Jan Marais, who he believes is a South African diplomat, but is in fact a Soviet false flag operative. SIS chief Sir Nigel Irvine eventually confronts Berenson with the truth and "turns" him, using him to pass disinformation to the KGB.