Anti-racism campaigners will stage a public rally today ahead of BNP leader Nick Griffin's appearance on Question Time.
Unite Against Fascism (UAF) will hold the meeting as last-ditch efforts to stop Mr Griffin appearing on the BBC1 show continue.
Wales Secretary Peter Hain wrote to the BBC's governing Trust yesterday appealing to it to reconsider its decision to allow the BNP to "the top table of UK politics".
He believes the party is currently illegal because it does not allow ethnic minorities to join.
Mr Hain appealed to the Trust as a last resort after BBC director general Mark Thompson rejected the Cabinet minister's arguments.
He wrote that Mr Thompson "shows no willingness or ability to genuinely review his own decision" and was "too close to the decision".
Yesterday ex-army chiefs General Sir Mike Jackson and General Sir Richard Dannatt accused the BNP of "hijacking" military symbols for their own advantage.
Referring to their accusations, Mr Hain said "new factors need to be properly considered afresh in balancing freedom of speech versus protection of the vulnerable".
With Question Time set for broadcast tomorrow night, Mr Hain is hoping for a quick response to his appeal.
He will also send a message of support to the UAF rally, which is being held tonight in central London.
The rally will feature poet and former children's laureate Michael Rosen, director of the Anne Frank Trust Gillian Walnes and Reverend and the Makers frontman Jon McClure.
Mr Griffin sparked outrage yesterday by comparing the British generals to Nazi war criminals and claiming Winston Churchill would join the BNP if he was still alive.
He also suggested his party was the most widely supported among rank-and-file soldiers.
In their letter to The Times, the generals wrote: "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."
But Mr Griffin, who was elected as an MEP earlier this year, told Sky News that his party was popular among the forces rank-and-file.
"I'm the one who talks to the families of young squaddies and large numbers of ex-servicemen and they all say that almost everyone at the coalface, fighting in Afghanistan, vote for the British National Party," he said.
Mr Griffin dismissed claims that he wanted a white-only military, but admitted that the Victoria Cross-holding black corporal, Johnson Beharry, would not be allowed to join the BNP.
Gen Jackson told The Independent: "I heard complaints that the BNP were being extremely offensive about Johnson Beharry.
"I looked into it, and found out that was indeed the case. I thought it was pretty appalling that a brave man like that should be insulted in this way."
And Major General Julian Thompson, the highly-decorated former commander of the Royal Marines, also speaking to The Independent, said: "The BNP trying to exploit the good name of our forces is pretty monstrous and the fight against this must continue. The fact that they had been maligning Johnson Beharry is dreadful."
Meanwhile, the BNP was facing an investigation by the Information Commissioner's Office after an apparent list of its members surfaced on the internet.
The spreadsheet posted on the Wikileaks site featured names, addresses and telephone numbers for some 16,000 individuals, including serving and former members of the military, doctors, and an airline pilot.
The party denounced the list as a "malicious forgery", saying it had no connection with "thousands" of the people named.
A Conservative Party spokesman described Mr Griffin's remarks comparing the generals to Nazi war criminals as "absolutely despicable and abhorrent".