The five are expected to fly into RAF Northolt, a Royal Air Force Base northwest of London, on Tuesday evening.
In Boston on Monday, Home Secretary David Blunkett said the five - Ruhal Ahmad, Asif Iqbal, Shafiq Rasul, Tariq Dergoul and Jamal al-Harith - would be released "over the next 24 hours," British news media reported.
"They, when they return, will of course go through the normal process of being interviewed by the counter-terrorism branch in London and the material that has been provided will be evaluated," he said at Harvard law school.
Four other British citizens will remain at Guantanamo Bay, however, where they are likely to face trial before a US military commission.
Up to 800 prisoners suspected of being Taliban or al-Qaida fighters are being held without charges indefinitely as "enemy combatants" at Guantanamo Bay, a US naval base at the eastern end of Cuba.
Britain announced on 19 February that, after months of discreet negotiations with Washington, the release of the five was imminent.
But while Blunkett said they posed no threat to national security, the government has left open the possibility that they will be arrested upon arrival under the Terrorism Act 2000 and held for questioning.
Blunkett (R) said the five might be
held for questioning
Up to 1 March, 88 detainees of various nationalities have been released from Guantanamo Bay and 12 have been transferred to their home countries for continued detention.
Blunkett said the four remaining Britons - Firoz Abbasi, Muazzam Begg, Martin Mubanga and Richard Belmar - were different cases because they had been arrested "in the combat zone" in Afghanistan.
"The evidence that has been picked up is best used in the United States, not in Britain," said the home secretary, whose speech in Boston was reported by Britain's domestic Press Association.
The release of the five coincides with a trip to Washington by a British delegation of intellectuals and human rights activists to condemn what they see as a lack of basic due process for all Guantanamo detainees.
On Monday, the Daily Telegraph newspaper quoted US officials as saying the remaining four British detainees are suspected of having links with Usama bin Ladin's al-Qaida network and considered too dangerous to be released.