LONDON (Reuters) - The government is considering offering extra safeguards over its plans to extend the time terrorism suspects can be detained without charge, the BBC reported on Thursday.

Ministers are considering extending the current 28-day limit police can hold suspects, possibly doubling it to 56 days.

The BBC, without citing sources, said they would now propose that an additional 30 days detention could be added under time-limited powers, taking the custody limit to 58 days.

The extension would have to be approved by the Home Secretary as well as by a judge.

The powers would expire after a few months.

The proposals follows suggestions by civil rights group Liberty and the Conservatives that there is no need to extend the detention limit as existing emergency laws already allow a further 30 days custody without charge.

On Wednesday, Prime Minister Gordon Brown said a new round of consultations on "detailed proposals" for pre-charge detention was beginning and he believed a cross-party consensus could be reached.

Ministers hope the extra safeguard of the Home Secretary's approval would overcome opposition in parliament to longer detention, the BBC said.

Two years ago, former Prime Minister Tony Blair unsuccessfully tried to extend the detention-without-charge limit to 90 days, but a House of Commons revolt stopped the proposal. The current 28-day limit was agreed instead.

"This is something driven by political rather than security concerns," Conservative Home Affairs Spokesman David Davis told BBC radio.

"(The government) hasn't shown an ounce of evidence as to why we should go beyond 28 days," he said.

"Unless it is something that is completely unpredictable and it is a state of emergency, you don't need the powers."

Labour backbencher David Winnick, who opposes longer detention, told BBC radio the proposals were being aired because the government knew it could not get approval for a straightforward extension through parliament.

"Only two years ago the government said it was absolutely essential to have 90 days -- we don't hear much about 90 days now," he said.

The development comes a day after Security Minister Lord West insisted he had not changed his mind over pre-charge detention after appearing to contradict himself over the issue in the space of a few hours.

(Editing by Steve Addison)