Plans to hold terrorists for more than 28 days are 'muddled and ill-advised'

Gordon Brown is warned today that his anti-terror laws could undermine the independence of judges and ultimately lead to the collapse of trials.

Controversial powers to allow MPs to vote on whether suspects should be held longer than 28 days are 'muddled' and 'ill-advised', a report by peers says.

The highly unusual procedure - included as a sop to Labour rebels - 'arguably risks undermining the rights of fair trial', according to the Lords' constitution select committee.

Under the Counter Terrorism Bill, Parliament would vote on whether to grant a temporary 'reserve power' for the Home Secretary, allowing courts to authorise detention for up to six weeks if there was an operational need.

Although this order would not be specifically about an individual case, politicians would 'have to tread a tightrope' to avoid prejudicing any trial.

'We are unconvinced that the Government have properly thought through this aspect of their proposed scheme,' the peers say.

The committee is also concerned that a judge could have to decide whether to extend a suspect's detention period within hours of a 'highly politically-charged debate' in Parliament.

Peers found that 'there is a risk that this will be perceived to undermine the independence of the judiciary'.

'Far from being a system of checks and balances, this is a recipe for confusion that places on Parliament tasks that it cannot effectively fulfil and arguably risks undermining the rights of fair trial for the individuals concerned,' the report says.

This 'elaborate' decision-making process would also give a far greater opportunity for legal challenges to arise, it is claimed.

'It is a weakness of the Bill, not a strength, that it is likely to lead to high-profile litigation during a time when the response to terrorism will be a matter of high controversy.'

Committee chairman Lord Goodlad, a Tory, said ahead of the report's release: 'Considering that any debate will be highly political in nature and any vote may well be whipped by the political parties, we are deeply concerned that the independence of the judiciary may appear to be undermined and that trials may be prejudiced.'

It is the latest blow to Mr Brown's plans to hold terror suspects for up to 42 days without charge.

He was forced to rely on the support of nine Northern Ireland MPs to win a knife-edge Commons vote on the measure and the Bill is almost certain to be defeated in the Lords later this year.

Last month, the former head of MI5 Baroness Eliza Manningham-Buller condemned the anti-terror laws as 'unworkable'.

The proposals have also been savaged by Lord Falconer, a Lord Chancellor under Tony Blair, and Labour's Lord Goldsmith, the former Attorney General.

Tonight shadow home secretary Dominic Grieve said: 'The committee joins a long list of experts who have condemned the Government's ill-thought through proposals for 42 days as both unfair and unworkable.

'The Government should abandon this measure and concentrate on delivering things that will actually make us safer - such as allowing the use of intercept evidence in terror trials and establishing a dedicated UK Border Police Force.'

LibDem home affairs spokesman David Howarth added: 'The 42-day proposal has everything to do with politics and nothing at all to do with the struggle against terrorism. It should be dropped immediately.

'The Government's insistence that Parliament will not have to decide individual cases is incredible.'