Tony Blair continued to talk tough over proposed anti-terror legislation today as his Home Secretary prepared a compromise deal to head off a humiliating government defeat.

While the Prime Minister launched a passionate last-ditch defence of plans to extend the custody limit for terror suspects to a maximum of 90 days, Charles Clarke took the pragmatic step of preparing an amendment which would water down the proposal.

Mr Blair remained insistent that the 90-day limit set down in the Terrorism Bill was essential for combatting the terrorist threat. He said that any compromise in the legislation would compromise public safety.

Meanwhile, Mr Clarke told reporters that the amendment would reduce the limit to an unspecified period of time, somewhere between the three months and the Tory proposal for a 28-day maximum.

Mr Blair said that the decision to lodge the amendment was simply a matter of procedure. He said that he would be attempting to persuade opponents to back the three-month guideline before the vote is taken after a final reading of the Bill in the Commons on Wednesday.

He told his regular monthly press conference that he remained convinced the case for the 90-day limit was compelling and scorned opponents for going against the advice of police, prosecuting authorities and - according to a Sky News/YouGov poll published today - 72 per cent of the British public.

He said: "Tonight here in Downing Street we have a reception for the emergency workers who dealt with the horror of July 7. Last week we remembered the dead and injured at St Paul’s Cathedral.

"We should never forget that this terrorist attack, the worst terrorist attack this country has ever had, happened just a few short months ago. Let me be very clear: this is not a plan dreamed up by me, or indeed with its origins in the Government.

"It is what the most senior police officers in the country, the Metropolitan Police Commissioner, the head of anti-terrorist policing, the Association of Chief Police Officers... it is what they have asked us to do as they battle to prevent further terrorist outrages."

Asked why the Government had tabled the last-minute amendment, he said: "Don't be under any misapprehension. We have got to do this as a matter of procedure, we have got to put this forward, but it is not the position we want and we will be persuading our people to come over to our side.

"We intend to use the time between now and Wednesday to try to get people to understand the importance of giving the police and our security services the powers they need to prevent terrorism in this country."

Conservatives and Liberal Democrats have both rejected the 90-day proposal saying it is an erosion of civil liberties. Backbench MPs last week pushed the Government to the brink of defeat over another controversial element of the Bill, which passed in the Commons of just one vote.

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