The 300,000 Conservative members might be denied a vote on who becomes its leader to prevent "civil war" breaking out in the party.
Tories opinion at grassroots level attacked the system of choosing the leader as a "shambles", and senior party sources admitted last night that the ballot of members laid down in the party's rules might not take place after all.
The rules, introduced under William Hague's internal reforms, say that a ballot involving all the candidates will be held among Tory MPs. The final two candidates left, after the one coming bottom in each round drops out, then go into a run-off postal ballot among party members to decide the winner.
Conservative Central Office is worried that the two-stage system could result in a leader being elected who does not command majority support among his own MPs. For example, Michael Portillo, who declared himself a candidate yesterday, could win the backing of 70 per cent of Tory MPs and Kenneth Clarke 30 per cent. But in the crucial ballot of party members, the figures could be reversed because Mr Clarke was backed by a majority of activists in the 1997 leadership contest. Mr Clarke would then win the leadership, even though he had been opposed by a majority of MPs.
Party sources admit that, if the front-runner in the MPs' election had a clear majority, then the second candidate would be put under enormous pressure to stand down. Activists at grassroots level are demanding a last-minute change to the rules. They want a simple "one member, one vote" ballot of members involving all the candidates.
The Conservative Campaign for Democracy is threatening to set up a website to allow Tory members to "vote" on all the candidates rather than on a shortlist of two chosen by MPs. John Strafford, the group's chairman, said last night: "You can't spend three years telling the members they will have a vote on the leadership and then say, 'Sorry folks, we've decided it, tough luck, but you can confirm it'. That is nonsense. The system is a shambles. If party members and MPs vote for a different leader, that would be a recipe for civil war."
Mr Portillo emerged as the front-runner to succeed Mr Hague after launching his campaign with the support of 11 members of the Shadow Cabinet.Mr Portillo said the Tories had to become more "understanding and moderate".
Mr Clarke is refusing to be rushed into a decision on whether to run and will "mull over" his options this weekend.Reuse content