Police can continue detaining terror suspects for up to 28 days without bringing charges, after MPs renewed the power last night.

The House of Commons agreed the extended detention without trial period should continue for at least another year in light of terrorist activity.

They also agreed to ban two more terror groups; Jammat-ul Mujahideen Bangladesh and Tehrik Nefaz-e Shari’at Muhammadi.

However, they did not ban Hizb ut-Tahrir, which was brought to public attention last week by David Cameron in prime minister’s question time.

The former home secretary John Reid said there was insufficient evidence to add Hizb ut-Tahrir to the list of banned groups.

The 28-day detention without charge period was brought in under the Prevention of Terrorism Act 2005. It was a compromise measure after the government failed to get parliament to agree to a 90-day detention without trial period.

In further reassurances to MPs, it was agreed the Commons would renew the 28 day limit annually, or it would revert to the previous 14-day period.

Terrorism minister Tony McNulty revealed only six people have been held for the full four weeks, three of whom were then charged.

Gordon Brown will publish a new terrorism bill in the autumn and it is expected he will again attempt to extend the detention without trial period.

Both the Liberal Democrats and the Conservatives have pledged to oppose such a move, sharing the concerns of civil liberties groups.

Renewing the 28-day period yesterday, shadow attorney general Dominic Grieve accepted that the UK has “moved radically away” from the time when it was sufficient to hold someone without charge for 48 hours.

But, he said he would like a return to the 14-day limit “if at all possible”. He pointed to the US, which only has a ten day limit before suspects must be charged or released.

Mr Grieve warned holding terror suspects for prolonged periods encouraged media speculation and risked prejudicing a future trial.

Nick Clegg, the Liberal Democrat home affairs spokesman, also reminded the government support for renewal did not mean the Lib Dems would support an extension beyond 28 days.

Mr McNulty said the government would welcome a “substantial debate” on new terror laws and “at the very least” a case had been made for the 28-day period.