MPs previously rejected attempts to extend the limit to 90 days

A "highly visible" uniformed force would bring together immigration and Customs officers, Gordon Brown said.

He also announced a review of allowing intercept evidence in court, and plans to raise from 28 days the time police can hold suspects without charge.

But the Tories and Lib Dems said any border force should include police officers, new resources and new powers.

Officers from the Border and Immigration Agency, Revenue and Customs and UKVisas will be brought together to create a "single primary checkpoint" for passport control and customs.

New uniforms do not make a new force

David Davis

Analysis: Terror consensus? Terrorism statements in full

Outlining his counter-terrorism strategy to MPs, he said the cabinet secretary had been asked to report back by October on how to implement the proposal "very soon".

But Shadow Home Secretary David Davis told the BBC the proposal was "a bit less than met the eye" adding: "New uniforms do not make a new force."

And for the Lib Dems, Nick Clegg said it was "a border force lite without police powers or the incorporation of the transport police".

Biometric visas

But Mr Brown said the new borders officers would have "immigration, customs and police powers to investigate and detain people suspected of immigration, customs and criminal offences".

He also said he wanted stronger measures to stop terrorism suspects arriving in the first place, through electronic screening of all passengers checking in and out of the UK.

I think it is a complete and utter nonsense, this idea that Parliament could act as a court

Nick Clegg

Lib Dems

Who guards UK borders? Q&A: Anti-terror laws

All visa applicants would require biometric visas from March 2008 and the existing "e-borders scheme" would be expanded.

An "all-party consensus" on the use of intercept evidence in court and questioning of suspects after they have been charged would be sought.

But the government looks set to press ahead with attempts to extend the period for which terrorism suspects can be held without charge, beyond the current 28 day limit.

Terror detention

Mr Brown said one option was to double it to 56 days, subject to parliamentary scrutiny and a judge's approval.

He said there had been 15 attempted terrorist attacks on Britain since 2001 and 30 people had been convicted so far this year.

Ministers say it is right to consider extending it because of the increasing complexity of some plots - but the Tories, Lib Dems and some Labour backbenchers have opposed previous attempts to do so.

For the Lib Dems Mr Clegg said the idea of parliamentary oversight of any extension was "complete and utter nonsense".

"What is Parliament supposed to do when the police are detaining someone without charge? They won't be given privy to all the information so I'm afraid I think a lot of that is a bit of a fig leaf."

'Terrorist recruiter's dream'

Mr Davis also indicated that the Tories would continue to oppose the moves, unless there was any new evidence that it was necessary.

Amnesty International's Nicola Duckworth said locking people up for 56 days without charge "amounted to internment" which had "devastating consequences" in Northern Ireland in the 1970s.

And Liberty director Shami Chakrabarti said it would act as a "terrorist recruiter's dream".

Home Secretary Jacqui Smith told the BBC the government recognised the "very real concerns about liberty", but added that terrorist plots were becoming more complicated, more international and police were having to go through hundreds of discs, computers and house searches abroad.

"The weight of opinion, not just from us but from others, suggests that we may well be getting to the point where 28 days will not be long enough to have done that investigation and to have charged somebody in order that you can then bring them to a conviction."

Other proposals announced include:

A new system of electronic exit controls at UK borders from 2009, so that passports can be checked against the "warnings index" in real time.

From March 2008 biometric visas to be extended to all visa applicants

A review of how to best protect crowded places, buildings and national infrastructure such as roads, railways, tunnels, bridges, water systems and utilities

UK watch list of suspects to be linked to the Interpol database of lost and stolen documents

£70m to help local councils and community groups with citizenship projects aimed at combating extremism

Consultation on tightening bail conditions and travel restrictions on terrorism suspects

Mr Brown also revealed that 900 shopping centres, sports centres and other venues where large numbers of people congregate had been assessed by counter-terrorism advisers.

And he said "additional protection" was needed for utility sites, crowded places and the national infrastructure, from roads and the railway to waterways.

Reviews on security measures at such sites would be on-going over the summer, he added.