There are at least 680 people being held at Guantanamo Bay
Tony Blair has been challenged to "put his foot down" and tell the Americans that the British men currently imprisoned at Guantanamo Bay should be tried in the UK.
Amid fears that Moazzam Begg and Feroz Abbasi will not get a fair trial, more than 200 MPs have now signed a parliamentary petition calling for the men to be repatriated.
Pressed several times on the issue at prime minister's questions on Wednesday, Mr Blair said the nature of the trials planned for the prisoners held at the base in Cuba had yet to be decided.
He promised to continue making "active representations" to the US Government to ensure the men had a fair trial.
On Monday Foreign Office Minister Chris Mullin said the UK had "strong reservations" about US plans to use military tribunals to try the two men.
Under the proposed trial arrangements it is understood that Mr Begg and Mr Abbasi will be denied the right to choose their own legal representation.
Seventy Labour MPs have signed the parliamentary petition and they have been joined by some Conservatives and Lib Dems, including former Tory frontbenchers Francis Maude and John Bercow.
The motion says the prisoners face a choice between pleading guilty and being given 20 years, or if they fail to do that and are convicted they face the death penalty.
The MPs also raise concern about the mental state of the two men after 18 months of incarceration in cages two metres wide and only 30 minutes of exercise twice a week.
Liberal Democrat leader Charles Kennedy took up those concerns on Wednesday, asking what the affair said about British influence in Washington.
"How long must it be that UK citizens are left to languish in this legal no-man's land?" asked Mr Kennedy.
And Labour MP David Winnick told Mr Blair: "Put your foot down, prime minister."
Fair trial appeals
Responding to those fears, Mr Blair told MPs there had to be a time when the detentions at Guantanamo Bay had to come to an end.
"There has to be no question about this at all," he said.
"Any commission or tribunal that tries these men must be one conducted within proper canons of law so that a fair trial is both taking place and seen to take place."
He went on: "The precise nature of these trials has not yet been formulated and therefore it is important that we wait and see whether our representations have been heeded."
Mr Blair said Britain's opposition to the death penalty was well-known.
Foreign Secretary Jack Straw raised the concerns over the treatment of Mr Begg and Mr Abbasi when he spoke to his US counterpart Colin Powell at the weekend.
There are at least 680 suspected al-Qaeda and Taleban members at the US naval base in Cuba.
Legal black hole
US President George W Bush decided on Thursday that six of them, including Britons Mr Begg and Mr Abbasi and Australian David Hicks, should face trial in a military tribunal rather than in a regular court.
The announcement sparked a wave of protest from human rights groups who said the tribunals would be a "legal black hole".
The UK government has already expressed concern about the men's access to lawyers, the standards of evidence and their rights to appeal in the case of any guilty verdicts.
On Monday, former cabinet minister and Tory MP Douglas Hogg said that America's reputation would suffer if they proceeded with the trials by tribunal which he described as "wrong" and "potentially unjust".
Mr Mullin responded: "In our view it's strongly in the interests of the US that these trials are
conducted in a credible and transparent fashion because it obviously will affect
the respect with which the US is held throughout the world."
The minister insisted that the government would not indulge in "megaphone diplomacy" in order to get its point across.