Plans to extend detention without charge for terror suspects suffered a major setback today when MPs studying the proposals concluded that the limit should not be increased.

Keith Vaz, the Home Affairs Select Committee chairman and Labour MP, said: “We saw no evidence that there was a case for extending the pre-charge detention beyond 28 days.

“The Home Secretary herself told us that only six out of 71 responses to the Government’s proposals on going beyond 28 days were supportive. This was a surprisingly small number.”

Jacqui Smith, the Home Secretary, is seeking to raise the current maximum of 28 days to 42 days, saying police need more time to scour encrypted computers and chase international leads in terrorism cases.

But members of the Select Committee said the Muslim community could come to regard the rules as a form of internment if ministers failed to prove why a longer period is required.

The Committee’s report concluded that other changes to the law would be a more effective way to improve prosecution rates and avoid the need to raise the pre-charge detention limit.

The MPs said, for example, that it was “ridiculous” that Britain still bars the use of evidence from telephone taps and other bugs - known as intercept evidence.

David Davis, shadow home secretary, said Ms Smith would be better off looking at new measures to track potential terrorists rather than continuing to try and force an extension of the limit through a reluctant Parliament.

“She should now focus her efforts on implementing practical measures, to get the best use of the current 28-day period - like our proposals for post-charge interview, the use of intercept evidence and enhanced sentences for withholding encryption keys,” he said.

The Committee’s findings are not binding but the report is likely to influence a Parliamentary vote on the proposals next year. The Liberal Democrats, Conservatives and numerous backbench Labour MPs are expected to vote against the measure.

Nick Clegg, Liberal Democrat leadership contender, said: “The fact that this is an all-party committee with a majority of Labour members on it surely spells the end for Brown’s misguided attempt to play tough on terrorism.”

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