Sir David Goodall who has died aged 84, was never more stretched as a diplomat than in the five years from 1982 to 1987, when as Deputy Secretary in the Cabinet Office and then as a Deputy Under-Secretary in the Foreign Office, he worked at the very centre of Margaret Thatcher’s Government.

The Anglo-Irish Agreement, which paved the way for the Good Friday Agreement and the Northern Ireland peace process, was signed by the Irish Taoiseach, Garret FitzGerald, and Margaret Thatcher on 15 November 1985. But the Prime Minister’s instincts were strongly against putting her name to it. Goodall, who with Robert Armstrong, the Cabinet Secretary, had led the British side in the tortuous negotiations, later admitted to Thatcher’s biographer, Charles Moore, that “We did a bit conspire … We did have moments when she was being terribly difficult and unreasonable.”