The party was not "embarking on a rightist crusade" when she forced Edward Heath to resign after the first ballot, he said. "It was, instead, preparing to use the only weapon available for the purpose of destroying Heath, who was hated by some but simply rejected as a loser by many more."
At 4pm on Tuesday 4 February 1975, Edward du Cann, chairman of the backbench 1922 Committee, announced that the stalking filly - as her campaign manager Airey Neave had described her - had beaten Mr Heath by 11 votes. She won 130 votes, Heath 119 and the no-hope candidate Hugh Fraser took 16. The election went to a second ballot.
The result was a triumph of deception. On the day of the ballot, Mr Neave and Sir William Shelton fed false information to the London Evening Standard. "Airey and I put on very long faces and we said, 'It looks as if Ted Heath is doing rather well, better than expected, it might just be one ballot'. And all the supporters of the people who could come in on the second ballot said, 'God, must have a second ballot.' So they voted for Margaret," Sir William told BBC Television's On The Record.
It was widely assumed that Mrs Thatcher would do well enough to force Mr Heath to resign and allow Willie Whitelaw to take over in the second round. But the momentum of her first-round lead carried her to a clear victory in the second ballot, winning 146 votes to 79 for Mr Whitelaw, who had held back out of loyalty to Mr Heath.
Mrs Thatcher claims she only stood because her mentor Keith Joseph had destroyed his chances by telling Birmingham Conservatives that too many children were being born to mothers at the lower end of the social scale.
John Redwood's detached intellectualism may make him more the Joseph than the Thatcher of the 1995 leadership poll. But there are striking parallels. Tory MPs face an agonising guessing game over the intentions of colleagues. Michael Heseltine's backers want Mr Redwood to do well enough to force a second ballot, but not to win. One of Mr Heseltine's followers said yesterday: "Abstentions will be very important. Look out for a large number of spoilt ballot papers."
In 1989, when Sir Anthony Meyer challenged Mrs Thatcher, he polled 33 votes and there were 27 abstentions, many of them spoilt papers. He told the BBC: "To my certain knowledge a certain number of people voted both for me and for Margaret Thatcher, thereby of course spoiling their ballot paper, but able to say to their constituency, 'Yes, I voted for the Prime Minister'."Reuse content