Nigel Farage says his party will not work with the BNP
UKIP says it has "unanimously rejected" an offer from the British National Party for an electoral pact at next year's European elections.
It says ex-tennis star Buster Mottram, a UKIP member who claimed to represent the BNP, made the "astonishing offer" at a meeting in London on Monday.
Under the deal the BNP would fight seats in the north while UKIP would focus on the south in the elections.
The BNP said a deal made sense. UKIP says it would not work with the BNP.
BNP leader Nick Griffin told the BBC it made electoral sense for the two parties to avoid standing against each other at the euro elections in June 2009.
He said he had spoken to a number of UKIP party members about the deal.
The UK Independence Party, which campaigns for Britain to withdraw from the European Union, says Mr Mottram has since been expelled from the party.
Although he was a party member, he was not on the national executive committee which met in Whitehall on Monday.
But a spokesman said that as a high-profile, well known member, nobody had challenged him about why he was at the NEC meeting.
They say he claimed to represent Nick Griffin. The party says he refused to leave the meeting after the offer was rejected and they called the police, after which he left.
UKIP leader Nigel Farage said: "There are no circumstances, no possible situations, in which we would even consider doing any type of deal with the BNP whatsoever.
"I'm simply amazed that the BNP thought we would even consider such a thing, given that we are a non-racist, non-sectarian party."