The Home Secretary David Blunkett will this week declare a state of "public emergency" in Britain to introduce internment without trial for suspected terrorists in this country.
The Home Secretary will provoke a storm of protest from senior Labour MPs, Conservatives and Liberal Democrats by announcing that Britain is derogating article five from the European Court of Human Rights to allow the detentions to take place. To do so, he will have to declare that Britain is under a heightened state of the threat of terrorism.
However, MI5 has secretly warned MPs that the tough new anti-terrorist measures to be unveiled by Mr Blunkett on Tuesday do not go far enough. Officers from MI5 met the Home Affairs Select Committee and told MPs they needed a new law concerning conspiracy to commit a terrorist offence, so as to plug loopholes that allow suspected terrorists to go free.
Their demands for tougher measures will set alarm bells ringing at Westminster, where MPs are preparing to attack some of the anti-terrorism proposals for going too far.
The Home Affairs Select Committee, which is rushing out a report on the new terrorism Bill, is expected to register its concern. Its Labour chairman, Chris Mullin, has told friends he has misgivings about indefinite detention without trial.
The Tory shadow Home Secretary, Oliver Letwin, will warn it is not in the national interest to detain suspected terrorists in British prisons.
A Tory spokesman said: "We don't think interning terrorist suspects in this country is a very good idea. If we end up with prisons full of suspected terrorists we are making ourselves a prime target. There would be a risk, either from direct attempts being made to free terrorists from these prisons, or attempts to take British subjects hostage and try to trade them."
Both the Liberal Democrats and the Tories are concerned at the speed at which the Bill is expected to go through Parliament and are calling for the legislation to be time-limited so that it would have to be renewed every year.
The Liberal Democrats are worried that some of the provisions may exclude some people from the asylum process altogether. The Tories are unconvinced of the need to make incitement to religious hatred a crime.
The committee meeting with MI5 officers was so secret that one member who missed it did not know it had happened.
MI5 officers gave two examples of suspected terrorists who had been stopped but not arrested as they had not broken the law. One man had £180,000 in cash at an airport, stuffed into his children's clothes. Another was carrying arsenic. "They said the man with the arsenic might have been planning to poison the water supply but had committed no offence so he was allowed to go," said one committee member.
The Home Office confirmed there was no law that could have led to detention in either case, although the Proceeds of Crime Bill allows the seizure of large sums involving crime. The sale of arsenic is tightly controlled but its possession is not an offence.
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