The British National Party has been thrown into pre-election chaos after a senior party official was arrested on suspicion of threatening to kill its leader, Nick Griffin.

Mark Collett, its publicity director, has also been accused by party chiefs of attempting to launch a "palace coup" against Mr Griffin.

The far-right party's senior members will hold an emergency meeting tonight at a secret location in the Midlands to discuss the crisis and Mr Griffin's leadership. He has faced criticism from within the party following his showing on the BBC's Question Time.

The bitter infighting has blown up as the BNP prepares its biggest ever general election drive, focusing on Mr Griffin's candidacy in the east London constituency of Barking.

The supposed plot was revealed in a leaked BNP internal document disclosing that Mr Collett had been "relieved of all positions within the party with immediate effect".

Mr Griffin had gone to the police after "serious allegations" came to light affecting the "personal safety" of the BNP leader and James Dowson, its senior fundraiser, the memo said.

The BNP document claimed: "We are able to say that Mark Collett was conspiring with a small clique of other party officials to launch a 'palace coup' against our twice democratically elected party leader, Nick Griffin. In order to create the artificial climate of disillusionment necessary for this to stand any chance of success, lies and unfounded rumours have been spread, and were planned to be spread much further."

The leaked document said there was "extensive circumstantial evidence" of an attempt to sabotage the party's local and national election campaigns, alleging sensitive party information had been leaked to damage its prospects. It also claimed there had been an "ongoing, co-ordinated and sustained hate campaign, feeding lies to certain anti-BNP blog sites".

It said: "All in all, we believe we have uncovered the most serious and dangerous threat to this party and its officers that we have ever witnessed."

In 2002, Mr Collett declared his admiration for Adolf Hitler and said he considered Aids a "friendly disease because blacks, drug users and gays have it", when he appeared in a Channel 4 documentary called Young, Nazi and Proud. In 2006, he and Mr Griffin were cleared of race hate charges linked to speeches that they had made before the 2004 local elections.

Mr Collett, 29, had been planning to stand in Sheffield at the election against David Blunkett, the former home secretary. He said yesterday: "I don't intend to say anything bad about the party that would compromise it in the run-up to an election. If I've been wronged, which I believe I have, I've still got no intention to undermine the party. I'm not someone who goes running to the press when I've got problems. I'm not going to say anything more, even about if I've been arrested."

Concerns about Mr Griffin's leadership had been growing within the BNP since his criticised performance on Question Time. He has faced internal fire for bowing to demands from the court to amend the party's constitution to admit ethnic minority members, and controversy over his expenses as a Member of the European Parliament.

A spokesman for the anti-fascist group Searchlight said: "Nick Griffin is constantly claiming he is the leader of a moderate, non-violent organisation. It is difficult to see how he can square that assertion with his statement to the police that his own head of publicity has been plotting against him."

Humberside Police said: "A 29-year-old man was arrested on Thursday on suspicion of making threats to kill. He was interviewed by Humberside Police detectives and has been released on police bail pending further inquiries."

The BNP came close to civil war two years ago after two organisers were accused of plotting a coup against Mr Griffin and sacked for "gross misconduct". They were backed by at least 50 activists and councillors.

But the BNP – itself born out of a split in the National Front's ranks in the 1980s – recovered and have since achieved two breakthroughs with the election of its first Greater London Assembly member in 2008 and its first two Euro MPs last year.

Mark Collett: 'They are out to destroy us whites'

Born in October 1980, Mark Collett grew up in Leicester in what he described as a "very working-class family". He disliked the burgeoning immigrant population, reportedly saying in 2002: "I went back there recently and it was worse than Leeds. Blacks everywhere, sari shops, jewellers, Indian restaurants. I hated that." His first dalliance with the BNP came after a speaker from that party was expelled from the Free Speech Society at Leeds University, where he was studying. When invited to a BNP meeting in Burnley afterwards, he felt "right at home". Collett's role as leader of the Young BNP was thwarted by an undercover documentary in 2002, in which he spoke of his admiration for Adolf Hitler and the UDA terrorist Johnny Adair. He was recorded saying that Aids was a "friendly disease, because blacks and drug users and gays have it". That led to a brief expulsion from the party. He was caught on The Secret Agent documentary in 2004 describing asylum seekers as "cockroaches". Of Asian men he said: "They don't go out mugging Asian grandmas, they don't go stabbing each other, they don't go trying to solicit sex off little Pritesh or little Sanjita, they go straight to the whites 'cos they are trying to destroy us and they are the racists." He and BNP leader Nick Griffin were prosecuted for alleged race hate offences and eventually acquitted.

Email extract: What the party told its members