Osama bin Laden’s former driver will be released from Guantanamo Bay today and sent back to Yemen, quietly ending a battle by military prosecutors to keep him locked up indefinitely as a dangerous terrorist.

Salim Ahmed Hamdan will serve out the remaining month of his detention in Yemeni custody before being released, averting the prospect of a damaging legal battle over his future that could drag on past Inauguration Day.

President-elect Barack Obama has vowed to close the military prison at Guantanamo Bay and the Pentagon’s decision on Mr Hamdan’s fate will spare him being forced to make that decision at a later stage.

But the complex machinations over Mr Hamdan’s detention highlight some of the problems the President will face in holding to that promise.

Mr Hamdan was due to be released in late December after serving a six-year sentence.

Prosecutors were furious when a military jury handed the former driver the light sentence, which amounted to only a few months with credit for time already served, after refusing plea bargains to push for life-time incarceration.

Bush administration officials insisted they had the right to detain Mr Hamdan beyond the end of the sentence in spite of the verdict, insisting he remained a threat.

But the Pentagon apparently baulked at the prospect of fighting their case all the way to the Supreme Court as a change of administration loomed and decided to return him to Yemen instead.

What to do with Guantanamo’s 255 or so remaining detainees presents an unenviable series of legal and practical problems for Mr Obama as he tries to close the institution he regards as a scar on America’s international reputation.

The Bush administration has long contended that countries like Yemen do not have the capacity to deal with returned detainees, be they those still in custody or others who are released but who may yet pose a threat.

Human rights lawyers also warn that America could be in breach of international law if it returns detainees to countries where they could be tortured or persecuted, a charge already leveled in the case of extraordinary rendition.

The return of Mr Hamdan, only the second Guantanamo detainee convicted on terrorism charges, suggests that the military jury may have been right when they decided he was not the dangerous terrorist prosecutors painted him as, but a hapless functionary of little significance beyond the identity of his boss.

Diplomatic sources said agreement had been reached with Yemen to hold Mr. Hamdan until his sentence expires on December 27, and keep him under close surveillance afterwards.

Concerns over Yemen’s ability to do so, however, have prevented the release of scores of other Yemeni detainees still in custody. Around 100 of Guantanamo’s inmates are from Yemen.

In closing Guantanamo, Mr Obama will have to weigh up a cocktail of considerations including how and if detainees might be tried on American soil, the risks in releasing potentially dangerous inmates and the safety of potentially innocent detainees on their return home.

Some believe the problem could prove insoluble. While Mr Hamdan may pose little threat, a hardcore of Guantanamo inmates do.

But the nature of their capture and detention means that much of the evidence against them is tainted and would not stand up in a civilian court.

Allegations of mistreatment and forced confessions will also complicate prosecutors’ cases.

The case of the 9/11 mastermind, Khalid Sheikh Mohammed, graphically underscores the system’s failures - revelations that he confessed after waterboarding may have ruined any hope of a conviction.

The biggest fear is that Guantanamo’s toxic legacy may force Mr Obama to introduce legislation allowing limited continued detention – a move as much at odds with the American judicial system as the Cuban jail itself.

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