Around 20 protesters, many wearing scarves to hide their faces, ripped a locked door off its hinges at one of London's main mosques and burst into the event organised by Britain's main Islamic lobby group, the Muslim Council of Britain (MCB), on Tuesday.
They pushed their way to the front of the room, stood on chairs and shouted slogans against the MCB, Blair, Jews, Christians, apostates and the entire British political system.
"Tony Blair can go to hell! Tony Blair can go to hell!," they chanted as television cameras turned on them.
The protest laid bare tensions within Britain's 1.6 million-strong Muslim community, where hardliners often garner publicity for radical opinions, including praise of al-Qaida leader Usama bin Ladin.
After about 20 minutes, the protesters - young, male, mostly bearded and wearing traditional Muslim dress - left of their own accord.
Tony Blair's Iraq policy seems to
have cost him Muslim support
In leaflets handed to reporters, they identified themselves as belonging to a group called The Saviour Sect.
The protesters said the MCB, an umbrella body of some 400 Muslim organisations throughout Britain, was a mouthpiece of the British government.
"Go to hellfire, Sacranie," one of them shouted at MCB leader Iqbal Sacranie, who tried to reason with the demonstrators.
They accused the MCB of doing nothing to help Muslims held in Iraq's Abu Ghraib prison while sending representatives to Baghdad last year to try, unsuccessfully, to secure the release of British hostage Kenneth Bigley.
They shouted slogans relating to Afghanistan and Guantanamo Bay as well as Iraq.
The MCB played down the protest and, when the news conference finally started, highlighted issues it says will be of concern to Muslims in the 5 May election.
Other moderate Muslims condemned the protest.
"We have to take on the Bakris, the Abu Hamzas and the bin Ladins of
Conservative Party candidate
Ali Miraj, standing as a candidate for the opposition Conservatives in Watford, north of London, said "we have to take on the Bakris, the Abu Hamzas and the bin Ladins of this world", referring to two well-known UK-based clerics as well as the al-Qaida leader.
Fiyaz Mughal, chairman of the opposition Liberal Democrats' group for ethnic minorities, said the protesters "in no way represent the history of Islam" and cited Bosnia and Moorish Spain as examples of societies where Muslims and non-Muslims had lived in peace.
Moderate Muslims are urging a big turnout from their community in the election, saying Muslim voters may hold the key to dozens of parliamentary seats.
At the last British election, in 2001, Muslims supported Prime Minister Tony Blair en masse, but his policy in Iraq and Muslim anger at their perceived stigmatisation by anti-terrorism measures mean Blair can no longer count on their support.