Tony Blair's plans to deport Islamic extremists and foreign terror suspects could fall foul of international human rights law because they face torture in their home countries, the United Nations has warned.
The verdict from Manfred Novak, the UN's special rapporteur on torture, came as the Government's problems deepened over its anti-terror crackdown.
It was examining ways of preventing the extremist cleric Sheikh Omar Bakri Mohammed from returning to Britain from Lebanon and was forced to abandon its threat to prosecute militants for treason.
The British Prime Minister said last week that ministers were attempting to win promises from 10 countries they would not torture deportees. But Mr Novak said assurances from countries such as Jordan and Algeria were worthless.
"If you deport people, whether they are British citizens or foreigners, to another country where they are subjected to the risk of torture, then this is absolutely prohibited under international human rights law," he told the BBC Radio 4 Today programme.
Mr Novak cited a recent example of a man deported from Sweden to Egypt, who was tortured in spite of promises by the Egyptian government that he would not be ill-treated.
"If a country usually and systematically practises torture, then of course they would deny they were doing it."
Britain has concluded a memorandum of understanding with Jordan that suspects who are returned will not be harmed.
Mr Blair has said Britain was "close to getting necessary assurances from other relevant countries", naming Algeria and Lebanon. The Government has not named the other states from which it hopes to win pledges.
They are thought to include Egypt, Tunisia, Morocco, Libya, Syria, Yemen and the United Arab Emirates. All retain the death penalty and, according to Amnesty International, there have been recent reports of torture in most.
Omar Bakri Mohammed, who praised the London suicide bombers as the "fabulous four", fled on Saturday. He has joint Syrian-Lebanese nationality and could be deported to either country.
Also likely to be deported is Abu Qatada, a Jordanian under house arrest after being released from Belmarsh prison.
Amnesty International recently highlighted reports that two Yemeni men were tortured in Jordan. They claimed to have been repeatedly hit on the soles of the feet while suspended upside down with hands and feet tied. It says torture is widespread in both Algeria and Lebanon.
Kate Allen, Amnesty's UK director, said: "The assurances of known torturers cannot be trusted. We have seen no indication of any monitoring to ensure these promises are honoured."
Speaking from Beirut, Omar Bakri Mohammed was defiant about returning to the UK. The cleric urged the Government to try to prosecute him if they believed he had broken the law.
"If there is a crime in the UK and my name has been mentioned I will be the first one to return to challenge all these allegations. There is no treason. I am not a British subject and I never committed any form of crime whatsoever," he said.
But in a sign of increasing confusion about his immigration status, John Prescott, the Deputy Prime Minister, suggested the radical cleric was free to return to Britain if he chose.
Mr Prescott, who is in charge of the Government while Tony Blair is on holiday, said: "I don't think he's welcomed by many people in this country, but at the moment he has a right to come in an out."
He added: "Enjoy your holiday. I hope it's a long one."
The Home Office is planning to tighten immigration rules before the end of the month to prevent Bakri from setting foot in Britain again. But it appears it is powerless to bar him before then.
A two-week consultation on expanding the circumstances in which foreign nationals could be deported or excluded from the UK is due to end next week. The new rules, which would not be subject to Parliamentary approval, could be enforced almost straight away.
If Bakri arrived after then he could be excluded as an undesirable; the Home Office would argue that he can safely return to Lebanon as he has recently been on holiday there.
Lord Falconer, the Lord Chancellor, today dismissed the idea that he and other radical clerics could be charged with treason as "extraordinarily unlikely".
Yesterday the civil rights organisation Liberty reacted angrily to the possibility of introducing special anti-terror courts.
- THE INDEPENDENTBy Marie Woolf, Nigel Morris