The shock defection of Alan Howarth, 51, the MP for Stratford on Avon - the first time a Tory has "crossed the floor" to Labour in this way - will reduce John Major's precarious Parliamentary majority from seven to just five.
The move, discussed over several weeks with the Opposition, also dashes the Prime Minister's hopes of a political relaunch at this week's Conservative Party conference.
Mr Howarth was on the Left of the Conservative Party, a former government whip and junior Education Minister. He also served as a vice-chairman of his party. He had been unhappy with the Government's education policy for some time, but his resignation letter to his constituency association chairman last night laid bare a damning general criticism of the Government's entire direction.
"You have been aware of my anxieties about developments in the Tory Party, and of my profound disagreement with a whole range of its policies," he said.
While the Tory party was clamouring for tax cuts for the comfortably off, teachers were being sacked because schools were inadequately funded. "Hostile and discriminatory attitudes towards foreigners and minorities exist in a wholly unacceptable way in the party. There is an arrogance of power and a harshness within the government which is damaging to our democracy."
Mr Howarth is a former pupil of Rugby School. He discussed the prospect of his defection in secret talks with Mr Blair over three weeks. The Labour leader urged him to "think long and hard" before quitting the Government's ranks and suggested the Stratford MP should "follow" Labour's "new Britain" party conference and make his mind up then. By Friday Mr Howarth had decided.
A Labour spokesman said last night that the ex-Tory's membership application was being speeded up so that he could take the Labour Whip at Westminster when MPs return from their recess on Monday week.
He added: "Mr Blair is delighted that an MP as conscientious, intelligent, and committed to social justice has decided that the Labour Party is the only party in Britain really addressing the needs and interests of the country."
The Conservatives'embarrassment will be deepened this morning when the party chairman, Brian Mawhinney, appears on the Frost Programme - for an unscheduled face to face encounter with the defector.
Mr Howarth, who separated from his wife Gillian after 28 years marriage in 1993, voted Labour in 1966. But he soon went into the ranks of the one-Nation Conservatives, moving into Smith Square to work for Willie Whitelaw before becoming the party's research director. He went into Parliament as member for Stratford on Avon in Mrs Thatcher's landslide victory of 1983.
There is no political precedent for last night's shock news. Defections have happened in the opposite direction, most notably Reg Prentice, the Labour MP who went over to the Conservatives and became a minister. But historians said nothing like this had happened before. Mr Howarth represents the political "catch" of his generation.Reuse content