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.
It follows the leaking of a BNP membership list containing 10,000 names and addresses last November.
A former party member was fined £200 in September after admitting publishing that document.
A BNP spokesman said he could not confirm that the latest 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."
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 Times newspaper 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.
The letter reads: "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 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.
He told the Times: "The BNP is claiming that it has a better relationship with the Armed Forces than other political parties. 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.
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 BNP leader Nick Griffin from the panel on BBC1's Question Time this 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 Time programme and our position remains as set out."
Mr Griffin is due to appear on Question Time alongside 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 against Mr Griffin's presence on the show at the BBC's Television Centre in west London when it is filmed on Thursday.
But an opinion poll at the weekend found voters backed the BBC by 63% to 23%.