UKIP's election campaign was a clear call to get Britain out of the EU

The idea is set to be discussed at the party's annual conference in October.

Such a move could cause particular problems for the Tories. UKIP leader Roger Knapman says some Conservatives have themselves asked for the truce.

The Tories say they want to be in Europe but not run by Europe and will not be affected by UKIP's decisions.

Growing threat?

UKIP fielded 434 candidates at the last general election but, buoyed by a strong showing at this June's European polls, is aiming for a full slate next time round.

Under the plan being pushed by some UKIP MEPs, the party would pledge not to stand at the next election against MPs of any party who signed a letter saying Britain should pull out of the EU.

There are MPs with small majorities who suddenly realise they do not have a hope of winning Roger Knapman UKIP

Mr Knapman said the party had such a policy in 2001 but no MPs took up the offer.

"They did not presumably feel much of a threat," he told BBC News Online.

That had now changed and some people in other parties had asked if UKIP would revive the idea, he said.

Asked about how many MPs had approached UKIP, Mr Knapman said he was "not talking about numbers but there are individuals".

"There are MPs with small majorities who, especially Conservatives, suddenly realise they do not have a hope of winning," he said.

'Coercion'

UKIP is currently divided between purists who believe the party should contest every seat and those who argue it is harsh to stand against MPs sharing their views on the EU just for the sake of it.

Mr Knapman himself said: "I think it is an issue worth pursuing. Nothing may come of it."

Nigel Farage, the party's leader in the European Parliament, said it was "crazy" to oppose MPs who shared UKIP's goal.

He thought a handful of Labour MPs and a dozen Tories would consider making the electoral compact.

But Eurosceptic Conservative MP Angela Browning said she would never sign up.

"I would certainly not be coerced by any organisation or party," she told BBC Radio 4's World At One.

'Clear Tory vision'

BBC political editor Andrew Marr said it would not be easy for Tory leader Michael Howard to allow anybody signing the UKIP letter to stand as a Conservative candidate.

The Conservatives say the question of disciplinary action against any Tory MP who signed the UKIP letter was "hypothetical".

A spokesman said: "We have set out clearly our vision of a modern and flexible Europe.

"Our approach is one that best serves Britain's interests and it will be the agenda on which we fight the next General Election.

"It is for the UKIP to make their own decisions about who they want to field as candidates and where. It is for the UKIP to make their own decisions. This will not affect our position."