Angela Browning, an Agriculture minister who has been in the thick of the BSE crisis, said in a campaign leaflet to the voters of Tiverton and Honiton that the euro would end the sovereignty of the nation state, and, as such, she would not support it.
She said the loss of sovereignty was threatened by a transfer of gold and currency reserves to the European Central Bank in Frankfurt.
But Mrs Browning pointed out that as the Conservative manifesto promised the Tories would not allow any further reduction in sovereignty, she was in step with party policy.
That remarkable view - a direct breach of the Government's wait-and-see line decided by Cabinet on 23 January - was then endorsed by Mr Major, who made light of it at his daily press conference.
However, he said only last month that ministers would not be allowed to break the line, and Labour and the Liberal Democrats were quick to attack the Prime Minister's retreat.
As Mrs Browning pointed out in a BBC radio interview, the manifesto says not only that the Government would negotiate and then decide on single- currency entry, but also that: "We will not accept other changes to the Treaty that would further centralise decision-making, [or] reduce national sovereignty ..."
Clearly enjoying Mr Major's support, the junior minister said in her Devon constituency that she was engaging in healthy and democratic debate. "We're not some Stalinist party like new Labour," she said.
But the debate was spreading across the length and breadth of the party, with other ministers threatening to break ranks and defy the Cabinet line.
In a BBC radio World at One interview, William Hague, the Cabinet minister who has been designated as a firefighting spokesman, said: "All candidates should be able to air their views in their election address. I would have thought that was a basic principle of parliamentary democracy."
Gordon Brown, the shadow Chancellor, said last night: "The Tories are now in chaos on the single currency, Mr Major's attempts to contain the revolt in his party have already fallen apart. He is being defied within his own Cabinet."
More ominous for Mr Major was the silence of Kenneth Clarke, the Chancellor of the Exchequer, whose support for the 23 January wait-and-see agreement was critical in keeping the Conservative Party together.
Paddy Ashdown, leader of the Liberal Democrats, said that if the Prime Minister failed to move he would effectively surrender Tory leadership to the Euro-sceptics.
Last night, senior Tories said they feared that the Tory truce could break apart - just as Labour's delicate pact over unilateral nuclear disarmament cracked open during the 1983 general-election campaign. But the Prime Minister urged his return to Downing Street at his formal adoption meeting in Huntingdon. "I want to stay to make sure we are not driven, without realising it is happening, into a centrist European system so that we could not get ourselves out again," he said.
n Labour has a 20-point lead over the Conservatives, according to a Gallup poll for today's Daily Telegraph. Labour is on 52 points, the Conservatives on 32 and the Liberal Democrats on 11.Reuse content