A cache of as-yet unpublished secret memoirs of the late Margaret Thatcher has been disclosed, revealing key details including about the 1982 Falklands War.

The 128-page, 17,000-word documents, handwritten a year after the bloody war with Argentina, were published for the first time after they were given to Britain in lieu of £1m of inheritance tax.

Hailed by the Arts Council England as the "single most significant historical document Margaret Thatcher ever wrote", no one but her late husband Denis was thought to be privy to them.

One of the key revelations in the memoirs was Thatcher's anger at then-foreign secretary, Francis Pym, for the latter's role in involving the Americans to end the conflict.

She wrote that Pym's peace proposal, which was agreed with the then-US Secretary of State Alexander Haig, was "totally unacceptable" and a "total retreat".

The private papers are being held at the Churchill Archives Centre, Cambridge.

The papers reveal that the former prime minister almost wept when she heard about the crash of a helicopter, which came down due to bad weather in the early days of the Falklands. However, Thatcher appeared to show no emotion when she ordered the sinking of Argentine cruiser the General Belgrano, in which 323 died.

"The next day, morning 3rd May, the submarine torpedoed the Belgrano which later sank. The two accompanying destroyers were not touched but were slow to pick up survivors from the Belgrano. We knew she had been hit but it was some hours before we knew she had sunk," wrote Thatcher.

Writing about the decision to send the British forces on a 8,000-mile journey to recapture the Falklands, she said: "The Task Force had been despatched with a speed and efficiency which astounded the world and made us feel very proud and very British."