The Conservative leadership contenders clashed bitterly over Europe yesterday as a senior party figure warned the Tories risked becoming Britain's third party if they do not embrace an inclusive agenda.
As the former chancellor of the exchequer, Mr Kenneth Clarke, described the European policy of his rival, the shadow defence secretary, Mr Iain Duncan Smith, as "a euphemism for leaving the European Union," the shadow foreign secretary, Mr Francis Maude, insisted the party must appeal to a wider audience or risk losing more voters.
Leadership ballot papers will begin arriving in the homes of 330,000 party members today and the decision by party leader Mr William Hague to endorse Mr Duncan Smith's campaign at the weekend was a crucial intervention.
It came as the results of an ICM opinion poll for the Sunday Telegraph showed Mr Duncan Smith was more popular than Mr Clarke among Tory voters.
According to the poll, 20 per cent said they were more likely to back the Conservatives if Mr Duncan Smith were leader compared with 14 per cent who said the same about Mr Clarke.
Firing the first shot in what will be a crucial few days for the candidates as party members fill out ballot papers, the pro-Euro Mr Clarke, who said he was not surprised by Mr Hague's decision, challenged Mr Duncan Smith to commit the party to permanent EU membership if he was elected.
Mr Duncan Smith's manifesto, which will be sent out to members this week, is expected to advocate looking beyond Europe and developing stronger economic, social and cultural links with the US.
Mr Clarke insisted the shadow defence secretary wanted to renegotiate European treaties and leave the EU if it could not be achieved; a policy that he claimed was a euphemism for leaving Europe.
"If he has now modified his views and is prepared to say that if he became leader we would never leave the EU, I would be very, very encouraged," Mr Clarke told BBC's Breakfast with Frost programme.
But the Eurosceptic Mr Duncan Smith strongly denied he would lead the Conservatives out of Europe.
A spokesman for his camp said: "Categorically, Iain has never, never contemplated Britain leaving the European Union. This is complete rubbish."
His campaign was boosted at the weekend by Mr Hague's endorsement, and some observers believe the former party leader, Baroness Thatcher, will publicly offer her support soon.
In a letter to Mr Duncan Smith's constituency chairman, Mr Hague declared he had a "particularly high regard" for the MP.
He acknowledged that while he had respect for Mr Clarke, the future for the Conservatives under his leadership would see the party "slide back into the divisions over Europe."
The outgoing party chairman, Mr Michael Ancram, who was knocked out of the leadership race early in the contest, predicted "chaos" in the party if Mr Clarke became leader.
Mr Ancram warned that if a general election were called at the same time as a referendum on British membership of the euro, the party would be faced with the prospect of its leader standing on the same pro-euro platform as the Prime Minister, Mr Blair.
Mr Clarke has made this move in the past and confirmed he was prepared to do so again at the weekend.
"We would have chaos and that would risk tearing the party apart. I think it is important to have a leader who speaks for the majority of the party on a major issue such as Europe and the euro," Mr Ancram told BBC's Breakfast with Frost.
Mr Maude, meanwhile, said both candidates could plunge the party into third place if they did not adopt Mr Michael Portillo's inclusive agenda.
Mr Portillo's former leadership campaign manager said the leadership contest was "a battle for the survival of the party".
"If we do not change ourselves and make ourselves appealing to a much wider group of people, rather than arguing about things which are of interest primarily to ourselves, we will fail and we will run the risk after the next election of becoming the third party," the shadow foreign secretary told BBC Radio 4.