Newly published former top-secret documents reveal that a direct communications link between Downing Street and Mikhail Gorbachev was not encrypted – despite the wishes of the government’s ‘technical experts’

Cost concerns resulted in senior officials deciding to leave a hotline between Downing Street and the Kremlin unprotected and open to eavesdroppers, according to newly released Cabinet Office documents from a file marked ‘top secret’.

The documents, released for the first time last week, show how wrangling over the cost of the special hotline for the British and Russian leaders resulted in it not having any encryption.

This meant that the line was vulnerable to being hacked by third parties.

Discussing the various options, Sir Patrick Wright, permanent secretary at the Foreign and Commonwealth Office, in a letter to Sir Robin Butler, cabinet secretary, on 14 June 1990, commented there is “no permanent link between the White House and the Kremlin. Rather surprisingly, when President Bush wants to call Gorbachev, it seems that the calls are made over insecure public lines (the Americans are not happy with this, but have said that they see no alternative for the moment). The Germans also use the insecure open system direct to the Kremlin”.

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A few weeks later, in a letter to Sir Robin dated 11 July 1990 and copied to Charles Powell, prime minister Margaret Thatcher’s private secretary for foreign affairs, Sir Patrick said: “our technical experts favour protecting the line”.

However, he added that a cost of £20,000 made the option of having encryption “increasingly unattractive” and said: “You will probably conclude in the light of this – and especially since neither the Americans nor Germans bother with any encryption protection – that the idea should not be pursued.”

Sir Patrick went on to ask: “I should be grateful to know whether you agree that the idea of protecting the line should be dropped.”

Powell, in a note on telephone communications with Moscow sent to Sir Robin on 12 July 1990, said: “I have seen Patrick Wright’s letter of 11 July to you about the proposed installation of a direct telephone line to the Kremlin, and his recommendation that we should drop the idea of protecting the line due to the considerable cost.”

He added: “In view of the snags, I agree that we should go ahead without encryption, at least initially. Certainly we could not find the funds from No.10.”

And on 27 July 1990, Sir Robin wrote to Sir Patrick: “I agree with you and Charles Powell that if the extra cost of encryption turns out to be as high as suggested in your letter, we should do without it.”