The Pro Euro Conservative Party, which will contest all 84 seats in next month's European Parliament elections, declared that they were "about the future of the Conservative Party."
John Stevens, a former Tory Euro MP and a founder of the rebel party, said: "We find it incredible that in five short years the party which was once the major pro-European force in British politics has become little more than a campaigning organisation for Eurosceptism. The time has come for pro-Europeans to take a stand against this suicidal process."
Mr Stevens said the new party, which wants Britain to join the single currency as soon as possible, would give a voice to disillusioned centre- ground voters. "This is their chance to protest against the hijacking of their party," he said.
Although leading Tory Europhiles, such as Mr Heseltine, are expected to distance themselves from the breakaway party, Brendan Donnelly, its co-founder, said: "The fact is that we are standing on his policies, we are standing on Ken Clarke's policy."
Yesterday it emerged that Mr Heseltine may decide to stay on as an MP after the general election to campaign for Britain to join the euro. He had been expected to retire as MP for Henley, where some Tory activists have been pressing him to stand down.
Mr Portillo fuelled the Tory debate by suggesting that Mr Heseltine's constant criticism of Mr Hague's policy had made him "irrelevant". Speaking on GMTV's Sunday Morning programme, Mr Portillo admitted Mr Heseltine was "a very big beast of the jungle" but said he should "knuckle under" and accept the Tory party's decision to rule out joining the euro in this Parliament and the next.
Mr Portillo praised Mr Hague for making the single currency a key issue in the Tory campaign. But he confirmed that he would turn down any approach by Mr Hague to become his party chairman, saying he was "enjoying my independence at the moment".
Despite the potential threat from the rebel party, Mr Hague is sticking to his Eurosceptic guns. The Tory manifesto for next month's elections will attack Labour and the Liberal Democrats for "scrapping the pound regardless of the economic and political consequences". Mr Hague will warn that signing up to the single currency would involve "huge risks" for Britain.
But in an election broadcast tonight, Labour will claim it "is setting the agenda for reform in Europe while the Tories are divided and extreme".
The Liberal Democrats will unveil their manifesto for the 10 June Euro elections today, promising a Europe that is "democratic not bureaucratic, decentralised not dictatorial". The Tories will follow tomorrow and Labour on Wednesday.
Margaret Beckett, the Commons leader and Labour's campaign co-ordinator, said the party would "ruthlessly expose the contrast between the strong leadership offered by Tony Blair and the weakness of the Tories' lame- duck loser, William Hague".