A document apparently listing thousands of British National Party members was posted on the internet today.
They include former senior members of the military, doctors and professors, according to the spreadsheet posted on the the WikiLeaks website.
The document gives names, addresses, home and mobile telephone numbers of apparent party members.
A BNP spokesman said he could not confirm that the list was genuine, and accused the “whole establishment” of trying to “derail” the party. He refused to confirm names featured on the roll, saying membership was a “private matter”.
"The timing of it, just before Question Time,is suspicious," the spokesman said. "The whole media is out to derail the BNP. "It is very difficult to hold on to these things nowadays, with the electronic media."
BNP leader Nick Griffin is due to appear on the BBC's Question Timethis Thursday.
The apparent leak of the membership list came as former military heavyweights joined forces to warn that the Armed Forces were in danger of being hijacked by far right groups.
The London Timesnewspaper reported that former Army generals had written a letter warning that political extremists had no right to share the Armed Forces' proud reputation. The letter, signed by former heads of the Army General Sir Mike Jackson and General Sir Richard Richard Dannatt, amongst others, said far-right groups were "fundamentally at odds" with the values of the British military.
The move follows the BNP’s tactic of using images of Winston Churchill and wartime insignia during recent European election campaigns.
“We call on all those who seek to hijack the good name of Britain’s military for their own advantage to cease and desist," the letter reads. "The values of these extremists - many of whom are essentially racist - are fundamentally at odds with the values of the modern British military, such as tolerance and fairness.”
Gen Jackson specifically attacked the BNP for using the army’s image.
"The BNP is claiming that it has a better relationship with the Armed Forces than other political parties," he told the Times."How dare they use the image of the army, in particular, to promote their policies. These people are beyond the pale."
The alleged BNP membership list includes retired majors and at least one former senior Royal Navy officer. There are at least 49 addresses in Northern Ireland on the list.
Mr Griffin said the party's critics had fallen "hook, line and sinker for a pack of far-left lies".
"I'm the one who talks to the families of young squaddies and to large numbers of young ex-servicemen, and they all say that almost everyone at the coalface, out there in Afghanistan especially, the rank and file, vote British National Party and support the British National Party," he told Sky News.
But James Bethell, director of anti-BNP campaign Nothing British, said there were no more than a few dozen Armed Forces veterans in the party.
“The military on the whole do a really good job of keeping the BNP out of the serving forces,” he said. “They are able to deploy a couple of dozen veterans at their parades. But it’s completely unrepresentative of the general attitude of both serving personnel and veterans.”
Meanwhile, the BBC has rejected a call from Cabinet minister Peter Hain to drop Mr Griffin from the panel on BBC1's Question Timethis Thursday.
Mr Hain, a long-standing campaigner against apartheid, wrote to BBC director-general Mark Thompson, warning that he could face legal action if he allows Mr Griffin to take part in the flagship political show. The Welsh Secretary argued that the BNP was currently “an unlawful body” after the party told a court last week it would amend its whites-only membership rules to meet discrimination legislation.
The Equality and Human Rights Commission had issued County Court proceedings over concerns that the membership criteria were restrictive to those within certain ethnic groups.
In a letter to Mr Hain, Mr Thompson responded: “According to the advice we have received, the British National Party is not prevented from continuing to operate on a day-to-day basis and its elected representatives continue to sit on councils and in the European Parliament.
“It remains the BBC’s obligation to scrutinise and hold to account all elected representatives and to do so with due impartiality.
“We are also advised that if there were to be any election - local or national - tomorrow, the BNP would still be able to field candidates.
"We therefore do not agree that the developments in the Central London County Court proceedings legally inhibit the BBC from allowing Nick Griffin to participate on the Question Timeprogramme and our position remains as set out."
Mr Griffin is due to appear on Question Timealongside Justice Secretary Jack Straw, representatives of the other main parties and black writer Bonnie Greer.
The BBC says Mr Griffin’s inclusion is based on obligations resulting from the party’s success in winning two seats in European Parliament elections this year.
Anti-fascist campaigners plan to stage a protest at the BBC’s Television Centre in west London during the filming of the programme.