The Defence Secretary, Des Browne, is leading a group of politicians and public figures who are boycotting an increasingly divided Oxford Union over the decision by its president to host a talk involving the Holocaust-denying historian David Irving and the BNP leader, Nick Griffin.
The event, entitled Free Speech Forum, which is planned for next Monday, has provoked uproar at the university and beyond. Some Oxford students say they have received death threats and fear they will be targeted by far-right groups.
More than a thousand people have signed a petition on the Downing Street website calling on Gordon Brown to condemn the talk. A protest rally in Oxford against what many students see as a cynical publicity stunt by the union's current president, Luke Tryl, is planned for tomorrow.
A string of politicians and celebrities have now pulled out of events at the world's most famous debating society, the credibility of which appears to have been badly damaged by Mr Tryl, a former chairman of the Halifax branch of Conservative Future, the Tory party's youth wing, who sees himself as a future prime minister.
Among those who have cancelled appearances are the television presenter June Sarpong, the Labour MPs Chris Bryant and Austen Mitchell, and Mr Browne. Sources close to Mr Browne said he did not wish to be "on the same programme as such people", and that "if he had known they had been invited he never would have agreed to speak in the first place".
Mr Tryl is said to be increasingly isolated in the society. One union insider said: "He has sacrificed so many great guests, simply for the sake of a fascist and a Holocaust denier to speak."
Denis McShane, the former Europe minister, pulled out of a meeting at the union last Thursday night after writing to Mr Tryl to object to plans for "two notorious anti-Semites to be given a platform at the Oxford Union". Mr McShane said: "To put four-star Jew-haters on to a prestigious platform like the Oxford Union is to validate modern anti-Semitism. If the Oxford Union has a right-wing ex-Toryboy president, he is entitled to invite whoever he wants. But those who think there should not be a platform for Jew-baiters are entitled to their view, too."
Asked about his position Mr Tryl, who describes himself as a "very liberal, modern person", said: "The BNP are in a minority, but they gain support when they say the liberals are silencing them." Pressed on BNP policies, however, Mr Tryl called them "abhorrent".
Yair Sivan, of the Union of Jewish Students, said: "There is no place for racists and fascists at universities ... Democracy does include the right to free speech, but it also includes the right to tell extremists they are not welcome – that democratic right would be one far more fitting for the Oxford Union."
The Oxford University newspaper, Cherwell, said students had received death threats from neo-Nazis. It is believed that BNP supporters are planning to "target" demonstrators at tomorrow's rally and at the event next Monday.
* October 1994
Kermit the Frog was invited, prompting accusations of "dumbing down". Kermit told the 1,000-strong audience: "The responsibility of representing an entire species rests upon my shoulders. Frogs usually only get in here by being in an experiment."
* May 1996
O J Simpson made his only public speech in Britain after the not guilty verdict in his trial for the murder of his wife and her friend.
* October 2000
Ann Widdecombe pulled out of a debate after her proposal of a zero-tolerance approach to cannabis use was followed by eight shadow cabinet members confessing they had smoked the drug.
* March 2001
Michael Jackson lectured on his plans for a universal bill of children's rights. The speech, made after a teenage boy alleged the singer had molested him, was met with barely muffled sniggers.Reuse content