But Mr Major said that Dame Angela Rumbold, a Conservative Party vice- chairman and the latest candidate to defy the leadership line on the European single currency, was not a member of the Government.
"Like every other backbencher she is entitled to express her views on an issue which may or may not, may or may not, come to fruition in unknown circumstances at an unknown time," the Prime Minister said.
Dame Angela, who is defending the highly-marginal Labour target of Mitcham and Morden, dismissed all criticism.
Michael Heseltine, Deputy Prime Minister, told his party's daily election press conference: "We are not going to conduct a witch-hunt - to borrow a phrase from the Labour Party - to the views of individual candidates."
But when Peter Lilley, the Euro-sceptic Secretary of State for Social Security, was asked if he could imagine circumstances in which he would back a single currency, he said: "I have such a fertile imagination, I can imagine almost anything."
Paddy Ashdown, the Liberal Democrat leader, said the Conservative Party was now at war with itself. "Be in no doubt this is the beginnings of the break-up of the Conservative Party," he said, "that's what we are seeing, it's ceasing to be a coherent and cohesive party that's able to follow through a coherent policy.
"Whatever your views about Britain's interests in Europe, a party at war with itself cannot prosecute those interests effectively."
Mr Ashdown said Mr Major was the captain left alone on the bridge of a sinking ship, and former Tory MP Emma Nicholson - who switched to the Liberal Democrats during the last Parliament - likened Dame Angela to a "loose cannon" on the deck of the same sinking vessel.
Gordon Brown, the shadow Chancellor, preferred at his press conference to cite the views of Edwina Currie, a Conservative candidate, who told the BBC radio Today programme: "It's a bit odd if policy is being made by candidates now and not by the people I thought were responsible for policy, which was the Prime Minister and the Cabinet."
But Mr Blair told Labour's daily press conference: "No-one knows where the Government stands. No one even knows where government ministers stand."
Mr Blair said that as far as Labour was concerned, there was "no insuperable constitutional barrier" to joining up to a single currency, provided it was the right thing to do in British interests, and had the support of a referendum
That was not the case with the Conservatives, he warned. "You focus for a moment on what would happen if these Tories get re-elected," Mr Blair said. "They'd be like ferrets in a sack; they'd be tearing each other part." Decision would not be taken on the basis of national interest. "Every single decision would be according to the state of play of the factions."