By Paul Reynolds
World Affairs correspondent, BBC News website
The release of the remaining four Britons from Guantanamo Bay could be seen as a gesture by President Bush to his war ally Tony Blair.
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It is particularly important to recall that two of the prisoners, Feroz Abbasi and Moazzam Begg, were named in June 2003 on a list of the first six prisoners who were to face military trials.
They therefore have changed from being in the top list of suspects to being considered safe enough to be freed.
This cannot easily be explained by the reviews of all Guantanamo Bay cases forced by the US Supreme Court decision last year that prisoners could take their cases to US courts.
Nor does the apparent decision by the United States to reduce the numbers of prisoners at the camp generally and to continue holding those of most intelligence value explain why two men once in the top six should now suddenly be set free.
The timing of these considerations has been helpful to the British demand for the prisoners' release - it gives the US a figleaf for the decision - but one cannot escape the conclusion that political considerations are likely to have played an important part.
In a statement to Parliament, the Foreign Secretary Jack Straw said that "had it not been for our alliance [with the US]", the prisoners would not have been freed. That is an admission in itself of the role politics and diplomacy have played.
Mr Straw hinted at Mr Blair's influence when he told the House of Commons that the releases followed talks in which the prime minister had taken part.
"Following contacts between the UK and the US, involving in particular my right honourable friend the Prime Minister and his office, and between US Secretary of State Colin Powell and me, the US Government has now agreed to the return of all four men to the United Kingdom. "
The Pentagon has suggested that there was a deal in which the UK and Australia, which has also had a prisoner freed, would
be responsible for the men.
"The governments of the United Kingdom and Australia have accepted responsibility for these individuals and will work to prevent them from engaging in or otherwise supporting terrorist activities in the future," it said in a statement.
This should all be put into the context of Mr Blair and the election he is likely to call in the spring.
He is trying to clear the decks of outstanding issues, especially those which spring from Iraq and the general war on terror declared by Mr Bush after 9/11.
Iraq he cannot change, given his commitment there. But he can remove some associated problems.
He has already got Mr Bush to agree to try to re-invigorate the Middle East peace process and to capitalise on the election of a new Palestinian leader. Mr Blair has organised a meeting in London in March to try to do his bit.
And with these releases, he has managed to get rid of another major issue.
He will be able to say to his critics that his closeness to Mr Bush does count.
There are precedents for special consideration for the British and the Australians. Mr Blair got Washington to agree earlier that no British prisoner should face the death penalty, as in theory they could have.
In March 2004, five other British detainees were also freed.
And there have been long negotiations about whether the men should be sent home to face trial in the UK or failing that, what kind of trial they should face in Guantanamo Bay.
The British government objected to the proposed system of military commissions, arguing that these lacked a proper independent element and a review by a civilian court.
For months these arguments were rejected by the United States.
Now they have all been set aside and the men are to be freed.