Michael Howard, the Euro-sceptic Home Secretary, told Alastair Stewart on GMTV's Sunday Programme that the agenda for June's European Union heads of government summit in Amsterdam "would indeed put our survival as a nation state in question. And if we send someone to negotiate on our behalf, at that summit, who doesn't want to be isolated in Europe, we are taking the most enormous risk.
"The things which we know Tony Blair would sign up to, the surrenders on the veto, more majority voting, the social chapter, would put us firmly on the federal path; firmly on the path to a European superstate."
But when that point was put later to Kenneth Clarke, Chancellor of the Exchequer, he disagreed. "We should be a leading member of the European Union," he told BBC1's On the Record programme. "We should not be imagining plots against us. I don't think the survival of Britain as a nation state is at risk because of our membership of the European Union. I just don't hold that view.
"What I do think is at risk is whether or not we can be a leading - or the leading - European power in the next century beyond the millennium."
As for the spectre that was being pushed by the Prime Minister last week - that a single currency could lead to a handover of tax and spending power to Brussels - Mr Clarke was equally dismissive.
"I am flatly against handing over control of tax to Europe, flatly against handing over control of public spending to Europe. So is every other European finance minister I know. No one has even suggested that," he said.
Gordon Brown, the shadow Chancellor, said: "Kenneth Clarke and Michael Howard have declared open war on one another. The two Tory parties are now not just out in the open - they are up and running, and at one another's throats."
Tory suggestions that Mr Blair was not up to the job of negotiating a good deal for Britain - the theme of last week's advertisement, showing the Labour leader as Helmut Kohl's dummy - were rejected yesterday by Sir Edward Heath, the former prime minister. "Everybody has got to learn about negotiations, of course," he told Sky News's Sunday programme. "But again, people don't accept it because they regard Blair as being a capable fellow."
However, John Major defended the advertisement on a Radio Forth phone- in, saying: "Politics is a robust trade and I dare say if there is one politician who has a right to say that because he has been on the receiving end of most the robustness in recent years, then you are talking to him at the moment."
Paddy Ashdown told BBC1's Breakfast with Frost that many moderate Tories were "dismayed and ashamed by the turmoil in their party", and he urged them to follow the lead taken by the two Commons defectors, Emma Nicholson and Peter Thurnham, and back the Liberal Democrats.
In a speech in Manchester today, Mr Blair will launch a personal attack on Mr Major's leadership qualities, saying: "A party divided against itself, with a leader trying to balance the factions in his party, cannot give any sort of lead. There are two Tory parties and John Major is in charge of neither of them."