Mr Hague committed the party to fight the next general election on a commitment to "save the pound", but was warned by former ministers that Mr Portillo was already staking out his campaign to force him to go further and rule out Britain's entry to the euro forever.
Launching a pamphlet by the Conservative Mainstream Group, Michael Heseltine warned: "Already, the Euro-sceptics are moving the goalposts. Mr Portillo is self- evidently now putting himself at the head of a campaign, called the Nation State, in order to move the Conservative Party to a position of `never'.
"That is a very great danger to William Hague ... He will need the centre of the Conservative Party before this issue is resolved; he will need us."
The former deputy prime minister and Kenneth Clarke, the former chancellor, will make it clear today in Conservative mainstream fringe meetings at the conference that the ballot has settled nothing and they will not give up their battle to keep open the Tory option of supporting Britain's entry to the Euro.
The ballot result came as no surprise, after Mr Hague effectively laid his leadership on the line. The turn-out was 58.9 per cent of the party - enough for the party leadership to claim legitimacy for the result - and only 15.6 per cent voted "no". More than half of the party's total membership of 344,157 either did not vote or rejected Mr Hague's policy.
The Tory leader today will use his opening speech to the conference to call for party unity, and draw a line under the Euro rows, which destroyed the Tories' last general election campaign. He dismissed the pro-European old guard, saying "as they say in Texas - big hats, but no cattle".
David Curry, the former minister for agriculture, told The Independent: "Michael Portillo is clearly setting out the ground for a `no' campaign. The time will come when William Hague will need the centre of the party to save him. I told him when I resigned from the front bench that the threat will come from the right, not the left. He now has to make up his mind: does he satisfy those on the right who are going to back Portillo?"
The Tory Reform Group, which is also active on the fringe this week, said that the result of the ballot was "dismal" for the leadership and "a blow to those hoping to destroy the validity of the pragmatic European view in the Conservative Party".
The ballot also failed to unite the rank and file.
Dave Jeffries, from Bexleyheath and Crayford, who voted "no", said: "It's not going to settle anything."
Ron Alcock, a director of a shoe company in Chelmsford, said he voted "yes" in the ballot to show loyalty to Mr Hague. "I am basically pro-European, but I wanted to see loyalty to the leader. That is the terrible dilemma were are in."
A former minister warned the Tory leader that he could be toppled by right wingers backing Mr Portillo, who want to go further.
Mr Hague said that the party "has spoken" and told the pro-Euro leaders they had a choice to back the leadership in focusing on the economy or "remain out of it - that is not a threat, it is not a promise - it is just the way it is".
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