Gordon Brown is planning to put the opposition parties on the spot by doubling the time that terrorist suspects can be held without charge from 28 days to 56 days.

Jacqui Smith, the Home Secretary, has been holding talks with her Conservative and Liberal Democrat opposite numbers to try to achieve consensus on measures to be included in a new counter-terrorism Bill, which will be announced in the Queen’s Speech next month.

The Prime Minister, who originally considered having a second try at introducing the 90-day limit that was defeated in the last Parliament, is understood to have settled for a much lower figure, and one that he believes he will be able to get through the House of Commons.

Ms Smith has yet to put a figure to David Davis, the Shadow Home Secretary, and Nick Clegg, the Liberal Democrat home affairs spokesman, and Home Office sources insist that she will not decide on a figure until consultations have been completed.

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But the attraction of going for the 56-day figure has grown considerably in the Government, particularly as ministers believe that Mr Davis would have problems in persuading Tory MPs to vote against a higher figure than 28 days. One minister said that David Cameron would be anxious to avoid Mr Brown monopolising a “tough on terror” mantle.

Mr Davis told The Times last night: “We have always said that if there was evidence to support this we would look at it carefully. So far, not only have we not had a shred of evidence to support this, but we have had an admission from the Home Secretary that there is not one new iota of evidence to support it and that any proposal to extend the term is because they ‘can imagine circumstances under which it would be necessary’.”

Ms Smith has seized on comments from Mr Davis and the campaigning group Liberty that suspects could be held under existing powers for 30 days under the emergency powers in the Civil Contingencies Act. She is arguing that they have therefore accepted in principle that suspects could be held for 58 days - 30 days plus the present 28-day limit - and that they should therefore be able to sign up to a bigger figure, perhaps 56 days, when the new Bill comes forward.

Ms Smith is also discussing safeguards for suspects held without charge, including weekly reviews by judges of all cases. She may also end the ban on questioning after charge, which would give the police more time for investigations to continue.

Ms Smith told MPs this week that there was “still some scepticism” about the proposals to extend the precharge questioning and detention period beyond 28 days. She said that there was no specific example of a terrorism case where police had needed longer than 28 days for questioning, but that the trend was towards more complex terrorist plots that could require a longer period of detention.

She said: “I accept that there has not been a circumstance in which it has been necessary up to this point to go beyond 28 days, and I think everybody has been very open about that. We have made a case based on what I believe to be the increasing complexity, the increasing international links and the increasing challenge of the investigation of the plots that are in place.”

Ms Smith highlighted the increasing complexity of cases by pointing to that of Dhiren Barot in 2004, where 274 computers were seized, compared with 400 computers in the alleged airline plot last year. There were about 2,000 computer disks, CDs and DVDs in the Barot case compared with about 8,000 disks, CDs and DVDs in the alleged airline plot last year, she told the Home Affairs Select Committee.

At the time of the arrests of three men, convicted in June this year for internet-based incitement to murder, the contents of the computers, hard drives and other media seized amounted to three terabytes (3TB) of data - the equivalent of almost a third of the entire content of the US Library of Congress, Ms Smith added.

She said: “Given the trend of evidence that we are seeing, and the range of people who are making the same argument that I am making - which is that we believe it is very likely in a very small number of cases that there will come a time when more than 28 days will be needed to question somebody - then it is reasonable and proportionate for us to be asking Parliament to discuss that now.”

This month Sir Ian Blair, the Metropolitan Police Commissioner, said that a detention period of 50 to 90 days would be “sensible” if there were judicial oversight. Control orders and police racism are driving young British Muslims to become suicide bombers, a drama to be shown next week to mark the 25th anniversary of Channel 4 will claim. Britz, depicting the transformation of an intelligent Bradford girl into Britain’s first female suicide bomber, is intended to “humanise” the July 7 London bombers who killed 52 people in 2005, said Peter Kosminsky, the writer and director.

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