Conservative leader Michael Howard has used a speech in Burnley to say he wants to confront the BNP head on and expose their "bigotry and hatred".
Howard sets out immigration policies
The Lancashire town was the scene of race riots just under three years ago and the Tory leader's visit has prompted accusations of opportunism.
But Mr Howard insisted that it was a mistake that no mainstream party leader has visited since the riots.
"The BNP are a stain on our democratic way of life," he said.
He also used his speech to stress the need for managing migration and asylum to stop extremists making capital out of the issues.
A Tory government would cut asylum seekers' benefits with any cash saved put into policing, he said.
And all asylum applications should be processed before the claimants reached the UK.
Since the local elections of 2002 the British National Party have gained seven seats on Burnley's council.
In his speech, Mr Howard said some people believed talking about the BNP only gave the party the oxygen of publicity.
But he argued: "I do not agree. It is important for politicians from mainstream parties to face up to extremists in any form, to tell people why we disagree with them and why they should be defeated.
"Let's not mince our words. The policies of the British National Party are based on bigotry and hatred. Its approach is entirely alien to our political traditions."
He underlined the criminal convictions of some BNP leaders, labelling the group as a "bunch of thugs dressed up as a political party".
Mr Howard, son of immigrants, pointed to his own father as one of the beneficiaries of Britain's tradition of welcoming people from all parts of the world.
And he accused BNP leader Nick Griffin of denying the existence of Nazi death camps.
"I happen to know that he is wrong about that," Mr Howard continued. "My grandmother was one of the millions of people who died in those camps."
Earlier, Mr Howard was asked why the Tories had fielded three fewer candidates than the BNP in the last council elections if they wanted to take on the party.
He conceded his party was not strong in Burnley and pledged greater effort in the future.
Burnley was hit by race riots in 2001
Phil Edwards, the British National Party's national press officer, branded Mr Howard's allegation that the BNP promoted bigotry and hatred as "complete nonsense".
He also attacked the Tory leader's comments about people in the BNP having criminal convictions pointing out that Jeffrey Archer, a former Conservative vice-chairman, had served a jail sentence for perjury.
"They have far more criminals in their party than we have in ours," he said.
He branded the Tory leader an "alien" before adding: "There are too many people of immigrant stock telling us what to do in this country."
The Tories were "paralysed by political correctness", he argued. "They are pandering to the ethnic minority vote and it's cynical and disingenuous."
Mr Howard also urged Tony Blair to impose transitional arrangements to handle migrants from new EU states.
Home Secretary David Blunkett is on Monday widely expected to unveil measures to limit access to benefits - but not the right to work - for new EU citizens from Eastern Europe.
Burnley's Labour MP, Peter Pike, urged the town's people not to be "used by the opposition in a cheap gimmick for publicity".
Shahid Malik, a Labour National Executive Committee member who lives in Burnley, said it was irresponsible for Mr Howard to talk about asylum in a town which had few asylum seekers.
Lib Dem peer Lord Greaves, who lives in the nearby town of Colne, warned Mr Howard not to "stir up trouble".
He said the main challenge to community relations and social cohesion was "not the three-year-old disturbances in Burnley - it is the activities of the BNP".