The history of the period is sometimes misremembered, refracted as it is through the prism of pro-EU reporting by organisations such as the BBC. On that day Mrs Thatcher was actually responding to eurosceptic concerns about her reliability. That was in doubt because she had agreed to so much integration earlier in her premiership. Norman Tebbit, David Owen, Tony Benn (with Michael Foot sitting on the bench behind him) and others tested her. Her attempts to offer a robust defence angered her Cabinet colleagues. Two days later, Geoffrey Howe resigned from the Cabinet, Michael Heseltine challenged Mrs Thatcher, and she resigned after failing to win decisively in the first ballot.

In the ensuing leadership contest, John Major (then seen as the Thatcherite candidate) triumphed over both Heseltine and Douglas Hurd. However, Major quickly sought to put the Tories back on a pragmatic path, flying to Bonn to assure the German government that he would put Britain where it supposedly belonged: "At the heart of Europe."

But there was a problem. It soon became apparent that Thatcher Mark II had been right and those who removed her wrong about Europe. Conservatives and others realised that Britain should never have had any part in monetary union, and hanging around on the edges trying not to cause a fuss would not prove very profitable either. Today she is also being proved right that the attempt to fold disparate European economies together into a single currency would be a disaster for the countries involved.

Within two years of Mrs Thatcher's fall, Britain had been blown out of the ERM, destroying the Tories' hard-won reputation for economic competence. Cameron was a young special adviser to Chancellor Norman Lamont at the time of the ERM crisis. He had a front row seat. The opt-outs that Major had painstakingly negotiated at Maastricht were insufficient to satisfy important elements in his party. Along with eurosceptics outside the Conservative fold who saw the party as an inadequate vehicle for their views, these dissidents had had more than they could tolerate of the diet of Tory pragmatism.