Controversial anti-terrorist measures should be streng-thened, Gordon Brown will argue this week in a clear signal that he is willing to reopen a battle between the government and Labour backbenchers over enhanced police powers.

Announcing an extra ?40m for the security services as this week's anniversary of the July 7 terror bombings in London approaches, Mr Brown showed his determination to face down opposition within the party to back an extension to the permitted detention period for suspected terrorists.

Last year, the government had to row back on a proposal to extend the period that police could detain terror suspects without trial from 14 to 90 days.

A compromise of 28 days was agreed after a rebel vote by 49 Labour MPs but Mr Brown believes the government needs to try again to extend the detention period to 90 days. However, a report by the Commons home affairs committee today argues there is no evidence to justify a detention period of longer than 28 days.

While acknowledging that the changed nature of the terrorist threat has made it necessary to allow police to arrest suspects early, it criticises the weak case made by the police to justify the new laws, which it said were drafted and presented to parliament in haste.

John Denham, the committee's chairman, said police responding to the changed terrorist threat needed the "important" tool of early arrest. But he warned that this represented a significant new legal development that needed explicit recognition.

"On an issue like this, the trust and confidence of the public and the Muslim community specifically is absolutely crucial. We cannot afford divisive arguments," he said. The committee recommended an independent scrutineer to review detention powers and advise ministers. It also said there needed to be judicial oversight of when it was appropriate to use detention.

A judge could also suggest alternatives to detention, such as tagging or control orders, which the committee supports. But control orders, which place suspects in effect under house arrest, have hit trouble. Six orders were quashed by the High Court last week when Mr Justice Sullivan said they were "incompatible" with human rights law. The government is to appeal.