As John Reid was speaking to an audience of Muslims in Leyton, East London, he was heckled by Abu Izzadeen, who is being investigated for allegedly discussing killing Tony Blair. Abu Izzadeen pushed his way into the meeting hall. Police said that Mr Reid was never in danger and that his armed protection officers were present.

The skirmish came as Mr Reid urged Muslim families to watch for signs of brainwashing in their children by radicals “grooming them to kill themselves in order to murder others”. He said: “Look for the tell-tale signs now and talk to them before their hatred grows and you risk losing them for ever.

“In protecting our families we are protecting our community . . . That is why I am asking you to be part of that fight for our common values, for this is the real conflict.”

The Muslim Council of Britain said that all parents, Muslim and non-Muslim, had a responsibility to ensure that their children were not misled by criminals and extremists. But it also urged the Government to recognise the impact of some of its policies, domestic and foreign, in contributing to the spread of extremist ideas.

Muhammad Abdul Bari, secretary-general of the council, said: “It is as though in response to the threat of global warming and the threat of rising water levels, the Government were to ask all of us merely to place sandbags outside our homes to prevent flooding. Surely, the more sensible way forward would be to tackle the causes of global warming.

“Similarly, in continuing to ignore the damage that some of our foreign policies have done to our national security, the Government is not facing up to a major contributory factor behind the rise of extremism.”

The Home Secretary was dismayed that his address to Muslim families was overshadowed by the extremists’ display. A Home Office spokeswoman said that although Abu Izzadeen had not been invited it was “an open community meeting”.

She added: “All appropriate security arrangements were in place on the day. There was no question of the Home Secretary’s safety being compromised at any time.”

But witnesses said that neither police nor Home Office officials knew who the intruder was. Abu Izzadeen was apparently not searched as he pushed his way into the hall.

Mr Reid’s appearance was not listed on the Home Office diary of events for the week and details were only given to the media on Tuesday afternoon. Waltham Forest council said that planning for the event began “about a week ago” and it drew up the guest list from among local community leaders, students and Muslim families.

Mr Reid faced a second protest from Anjem Choudary, the leader of another banned Muslim group, who is also facing investigation over his alleged remarks at the weekend that the Pope deserved to be killed for his comments about Islam.

Mr Reid’s speech received a hostile response from a number of Muslim groups. Imran Waheed, a spokesman for the Hizb ut-Tahrir group, which the Government has threatened to outlaw, said that the Home Secretary was making “the ridiculous demand that Muslim parents spy on their children”.

Massoud Shadjareh, chairman of the Islamic Human Rights Commission, said that Mr Reid’s demands were “unrealistic and not demanded from any other community.”

The televised protests raised questions as to why none of Britain’s “preachers of hate” has been prosecuted under the Government’s new terror laws. After the July 7 London bombings last year Tony Blair promised to act against militants, pledging to deport extremist imams from abroad and deal with British-born radicals who encouraged violence. Although Spain, Italy, France and Germany have expelled a number of foreign preachers, Britain has yet to deport anyone.

Patrick Mercer, the Conservative spokesman for homeland security, said: “Tony Blair was right to say he would deal with them. His intentions were spot on but as usual his execution is appalling.”

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