Nigel Farage is facing a rebellion within UK Independence Party ranks over suggestions of an electoral pact with Eurosceptic Tory MPs.
The Ukip leader has raised the prospect of its candidates running on a joint ticket with like-minded Conservatives at the next general election. The idea has also been floated by prominent Tories as a way of averting a split among voters on the centre-Right.
But Mr Farage is facing strong resistance from senior party figures who warn the move would alienate disillusioned former Labour voters contemplating switching allegiance to Ukip.
And they predict any attempt by Mr Farage to support local deals between Ukip and the Conservatives would run into strong opposition in the party's ruling national executive.
A senior party source told the Independent: "People might call us 'Nigel Farage's Ukip', but they forget the party is bigger than him.
"He would face a hell of a struggle to persuade colleagues over the wisdom of the move. I am dead against it. In my area there are plenty of Ukip activists who used to campaign for Labour - how would they react to a deal with the Tories?"
Mr Farage has said any pact would depend on David Cameron stepping down as Tory leader - and no decision would be made until after next year's European elections. But a spokesman for him yesterday insisted he had not ruled out the idea under all circumstances.
Opponents of the move within Ukip ranks argue that any tie-up with the Tories could prove toxic in urban constituencies in the north of England where the party has performed strongly in recent months. Their argument was underlined after Ukip came a strong second this week in a council by-election in Salford in a ward it had not even contested previously.
Stuart Parr, the author of Bloggers for Ukip, said: "An electoral pact with the Tories might give the Tories a boost, but it would fatally damage Ukip and one thing we are certainly not here to do is to make the Tories or any other party more electable."
Another site contributor said: "A Tory-Ukip pact would all but destroy the prospects we have with Labour voters. It would kill our advance in the Labour dominated areas of the North (and by extension Wales and Scotland) absolutely stone dead."