MI5 is to draw up detailed contingency plans for the return of five Guantanamo Bay inmates to Britain, including one accused of having trained at al-Qaeda camps to carry out terrorist attacks in the West.

David Miliband, the Foreign Secretary, and Jacqui Smith, the Home Secretary, announced a policy U-turn yesterday by formally asking the US for the release of the five from Camp Delta. The men will be placed under surveillance and could have terrorist control orders imposed on them if they are thought to be a threat to national security.

A United States military indictment alleges that Binyam Mohammed received firearms and explosives training alongside the shoebomber Richard Reid, was lectured by Osama bin Laden and was given a terrorist mission by Khalid Sheikh Mohammed, the architect of the 9/11 atrocities.

Mr Mohammed, 29, an Ethiopian who converted to Islam while living in London in the late 1990s, denies the allegations and says that he was charged by the US military only after being tortured at a CIA “ghost prison” in Morocco. His military trial ground to a halt after the US Supreme Court declared it illegal.

But the return of the men — which Washington indicated was likely in the near future — will present ministers with a security headache.

Whitehall sources indicated last night that all the detainees would be subjected to surveillance checks when they arrived back in Britain. MI5 and MI6 were both consulted before the policy change was announced but security sources would not say whether any of the five poses a significant threat. The authorities are also likely to examine the possibility of deporting the five onwards to their countries of birth.

Only one man named in Mr Miliband’s letter to Condoleezza Rice, the US Secretary of State, has so far been deemed fit for release by the American military. The others still bear the stamp of “enemy combatant” imposed by controversial military tribunals held at the internment camp at a US naval base in Cuba. The man cleared is Jamil el-Banna, a Jordanian refugee with five children in London, who was detained by the CIA in The Gambia in November 2002. But Mr Mohammed’s release has not been declared safe, nor has that of the other three men identified by Mr Miliband. All three have refugee status or leave to remain in Britain. They are:

— Shaker Aamer, 40, a Saudi citizen captured by the Northern Alliance in Afghanistan in 2001;

— Omar Deghayes, 37, a Libyan refugee detained in Pakistan after fleeing over the border from Afghanistan;

— Abdennour Sameur, 34, an Algerian picked up by the Pakistani Army after allegedly being sent from Finsbury Park mosque for jihad training in Afghanistan.

The Conservatives demanded to know last night what the Government proposed to do. Damian Green, the Shadow Immigration Minister, said in a letter to Ms Smith: “The Government presumably has some knowledge about the individuals involved and will have considered whether they present any threat if returned to Britain.

“Can you confirm, on the information you have, either that the individuals present no risk to British security or that the necessary measures have been taken to ensure that they will pose no threat on return to this country?

The State Department welcomed Britain’s intervention. A spokesman said: “It is useful when countries in the international community agree to share the burden of managing the threat posed by the enemy combatants detained at Guantanamo.

“Although many have called for the closure of Guantanamo, few states have offered a viable alternative for what to do with these dangerous men held there. We appreciate the UK’s offer to take responsibility for the five detainees.”

Clive Stafford-Smith, legal director of Reprieve and lawyer for some of the detainees, said: “I congratulate the Brown Government on a huge step in the right direction. At last we are seeing an ethical foreign policy: action rather than words. Respect for human rights and justice are our first and best protection against terrorism.”

The Government’s announcement reversed the previous policy of not intervening in Guantanamo cases where the detainees were not British citizens. The announcement was made just 48 hours before Ms Smith had to comply with a High Court deadline to say whether or not she was prepared to accept Mr el-Banna’s return to Britain. His lawyers had gone to court seeking a judicial review of the Government’s refusal to allow him to return to London to live with his family.

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