Osama bin Laden’s former driver was sentenced to less than six years in prison last night, an extraordinarily light sentence and the latest blow to the Bush Administration’s efforts to justify its highly controversial military tribunal system at Guantanamo Bay.

The sentence of five-and-a-half years for Salim Hamdan, handed down by a jury of US military officers in the first war-crimes tribunal to be held at Guantanamo Bay, fell far short of the 30 years incarceration sought by Bush Administration lawyers and means that the Yemeni is eligible for release in just five months.

As soon as the sentence was issued, however, the Pentagon made it clear that it had no intention of releasing Hamdan. It says that it retains the right to keep him in prison for an indefinite period because he has been classed as an “unlawful enemy combatant”.

Such intransigence in the face of last night’s sentence handed down by an all-military jury with rules of evidence that favoured the prosecution will bolster the case made by civil rights groups, and much of the international community, that holding Guantanamo Bay detainees indefinitely is unjustifiable, particularly after they have been tried. With Mr Bush leaving office in six months the problem of what to do with Hamdan — and the other detainees — will fall to his successor.

The sentencing hearing came after Hamdan was convicted on Wednesday of providing support to al-Qaeda, but was acquitted of the more serious charge of conspiring to attack civilians. It was a verdict that meant that the Administration was unable to prove that he had helped to plot and carry out attacks.

Before the sentence Hamdan expressed sorrow and apologised over innocents killed — an apparent reference to the September 11, 2001 terror attacks. He appealed for leniency in the first US war crimes trial since the Second World War.

Wearing a charcoal sports coat and white turban, Hamdan, speaking in Arabic, said through an interpreter: “It was a sorry or sad thing to see innocent people killed. I personally present my apologies to them if anything what I did have caused them pain.”

When the verdict was handed down by the six-member jury, he said: “I would like to apologise one more time to all the members and I would like to thank you for what you have done for me.”

The military judge told Hamdan: “I hope the day comes that you return to your wife and daughters and your country, and you’re able to be a provider, a father and a husband in the best sense of all those terms.

Hamdan responded: “God willing.” Prosecutors had insisted that he remained a dangerous man and that he should get at least 30 years behind bars for his work for bin Laden, who remains at large nearly seven years after the worst terrorist strikes on US soil.

Before the jury began to confer, defence lawyers said that Hamdan posed no danger as a former driver, regretted his links to bin Laden and suggested that he should be sentenced to no more than 45 months.

“He made a series of bad decisions,” Charles Swift, his defence attorney, said. “Looking back they are terrible decisions.”

Hamdan, believed to be 40, was arrested at a roadblock in Afghanistan in November 2001. He had two surface-to-air missiles in the car. The prosecution said that between 1998 and 2001 he had delivered weapons for al-Qaeda and was part of the inner circle of bin Laden.

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