Planned military tribunals for terror suspects held at Guantanamo Bay are unacceptable, the UK's attorney general has said.
The detainees have been held for two years without trial
Four British men are still being held at the camp in Cuba.
In a speech on Friday, Lord Goldsmith argued there can be "no compromise" on certain principles and the US tribunals would not offer a fair trial.
The UK Government has always voiced reservations over the trial plans. Lord Goldsmith is underlining the point.
Defence Secretary Geoff Hoon said the government would listen carefully to the attorney general's comments but stressed that as a sovereign state the US would steer its own course.
He said the government had made its position clear to the US over the Guantanamo situation and would continue to do so, but the UK could not always guarantee to influence events.
BBC Pentagon correspondent Nick Childs says the US authorities insist the military tribunals, or commissions, will be fair and will comply with international standards.
Officials cite presumption of innocence, proof beyond a reasonable doubt, the promise of no adverse inference from refusal to testify, the ability to call and examine witnesses and representation by a "vigorous" defence as safeguards.
But our correspondent says critics are concerned that the tribunal process will be controlled by the Pentagon and that defendants may not be allowed to see secret evidence against them.
Downing Street meanwhile stressed that plans to use tribunals to try detainees were on hold.
A spokesman said: "The position is that we
are continuing to work to resolve the situation with regard to the four remaining British detainees.
"The attorney general's remarks haven't come as any surprise to us because we
have always said British detainees should be treated in accordance with
international standards, and discussion are continuing."
For the Lib Dems Menzies Campbell said the issue had the "potential to cause major damage" to Anglo-American relations.
He added: "But the British Government cannot shirk its responsibility to its own citizens. If the positions were reversed the clamour from the White House and Congress would be loud and persistent."
Amnesty international's UK director Kate Allen said: "The important thing now is that the UK government seriously steps up pressure to speedily secure proper trials or the immediate release of everyone held in Cuba."
Whitehall officials say they do not see the speech as the minister ramping up British rhetoric on the issue.
But former Labour attorney general Lord Morris said Lord Goldsmith's comments showed how "fed up" he has become with the situation in Guantanamo.
Lord Morris told Today: "In this country we wouldn't put up with it for one minute if there were prisoners in jail for 18 months who had no access to lawyers."
Louise Christian, who represents two of the British detainees held at Guantanamo said she was "delighted" the attorney general had "come out" and made his remarks.
She asked what other government ministers were doing to secure the repatriation of the remaining UK citizens being held at Camp Delta.
President Bush announced plans for the military commissions to try 600 detainees at Camp Delta last July.
Britons Feroz Abbasi from
Croydon, south London, and Moazzam Begg, from Birmingham, were on the initial list of six to be tried under the controversial set-up.
But they have now been taken off the list while discussions continue between the US and UK about the future of all the British detainees.
Five other Britons were returned to Britain in March and were quickly freed without charge.
Lord Goldsmith and Foreign Secretary Jack Straw have previously said the US should either try detainees in accordance with international standards or return them to Britain.
In his speech, Lord Goldsmith said: "While we must be flexible and be prepared to countenance some limitation of fundamental rights if properly justified and proportionate, there are certain
principles on which there can be no compromise.
"Fair trial is one of those - which is the reason we in the UK have been
unable to accept that the US military tribunals proposed for those detained at
Guantanamo Bay offer sufficient guarantees of a fair trial in accordance with
Lord Goldsmith argued the international community needs to be "flexible and
imaginative" in the fight against groups like al-Qaeda.
But he added the right balance must be struck between security and individual freedoms.
Lord Goldsmith delivered his speech first in London and he will repeat it on Friday night in Paris to France's highest court, the Cour de Cassation.