A joint statement on two Britons being held as suspected terrorists at Guantanamo Bay in Cuba is expected from Tony Blair and George W Bush on Friday.
Moazzam Begg and Feroz Abbasi are among the Britons held
It follows private discussions between the British and American leaders about the future of Moazzam Begg and Feroz Abbasi, who are among nine Britons at Camp Delta.
There are concerns among civil rights campaigners, and some cabinet ministers, that the men might not have a fair trial when they go before a US military court, which has the power to sentence them to death.
Comments by the US president, during a joint press conference with Mr Blair, that the prisoners in Guantanamo Bay are "bad people" will have intensified those concerns.
Mr Begg and Mr Abbasi are among the first group of terror suspects at Camp Delta due to face trial.
The Foreign Office said it is continuing to press the US for a decision about the future of all the Britons held.
A spokeswoman told BBC News Online: "Indefinite detention without charge and trial is not a satisfactory situation."
On Thursday, Mr Bush promised to "work with the British government" on the Guantanamo Bay men.
He went on: "These were illegal combatants. They were picked up off the battlefield aiding and abetting the Taleban.
"The only thing we know for certain is that these are bad people."
The description of the men as "bad" was attacked by Mr Begg's father, Azmat.
He told GMTV: "If he is found guilty here I will say that my son is a bad man but if he's tried there under military jury or in America I will have a different opinion altogether."
Mr Begg senior said his son has been deprived of human rights during his 18 months in Cuba and that he will die unless he is returned to the UK to face trial.
He told BBC News Online: "This country is the mother of justice - how can they say our laws are not good enough?"
British Camp Delta prisoners
Shafiq Rasul, 24, of Tipton, West Midlands
Asif Iqbal, 20, of Tipton
Ruhal Ahmed, 20, of Tipton
Martin Mubanga, 29, from north London
Jamal Udeen, 35, from Manchester
Richard Belmar, 23, from London
Tarek Dergoul, 24, from east London
Moazzam Begg, 35, from Birmingham
Feroz Abbasi, 23, from south London
Stephen Jakobi of Fair Trials Abroad also attacked President Bush's description of the detainees as "bad people", describing it as "the end of any prospect of a fair trial".
He said: "Unless Tony Blair can announce a radical change of policy on mode of trial
today he will be assisting in a formula for dishonourable surrender of
sovereignty and the duty to protect his own citizens' human rights."
Home Secretary David Blunkett is thought to favour a civil trial in America, while Foreign Secretary Jack Straw has said he wants the men to be repatriated to Britain for trial.
Foreign Office Minister Chris Mullin has said the UK had "strong reservations" about US plans to use military tribunals to try the two men
However there are concerns that should the men be brought home for trial, the Crown Prosecution Service would have difficulty mounting any prosecution at all.
More than 200 MPs have signed a parliamentary petition calling for the men to be repatriated.