The UK Government was too slow to start investigating claims that the US has secretly flown terror suspects through the UK, says a powerful group of MPs.
Allegations on rendition flights continue
The Commons foreign affairs committee says ministers must tell the US it is "completely unacceptable" to fly suspects abroad to be tortured.
Prime Minister Tony Blair said he knew of no evidence the US had been flying suspects through UK territory.
He said people should not assume the US was doing so without asking permission.
Ministers say they have not been asked by the current US Government to let suspects be flown through UK territory.
But MPs raised concerns in their annual human rights report.
They said: "We conclude that the government has a duty to enquire into the allegations of extraordinary rendition and black sites under the Convention against Torture, and to make clear to the USA that any extraordinary rendition to states where suspects may be tortured is completely unacceptable."
The MPs said they were pleased the UK had asked for more information at European Union level.
But they said they seriously regretted that ministers had not asked the US directly for information.
"Only after prodding by European Union member states has the government made any effort to investigate serious allegations," said the MPs.
Committee chairman Mike Gapes said he was irritated by the way the MPs had been treated, with information given to other people rather than as evidence to its inquiry.
"What comes out puts the thing in the worst possible light," Mr Gapes told BBC Radio 4's World At One.
"If there is no evidence of any kind then the way they have handled it has not imbued public confidence."
In recent months there has been a wave of allegations about so-called "extraordinary rendition" - moving terrorist suspects to other states to be interrogated.
Air traffic controllers have said that two US planes suspected of being used to carry terror suspects have crossed British airspace about 200 times in the last five years.
But at his monthly news conference Mr Blair said: "There is no evidence that I know of that any of these 200 flights have been used for rendition."
The US had an arrangement with the UK that it would ask for permission to fly suspects through British territory - and had made two requests in the 1990s, he said.
"I'm not prepared simply to assume that they are breaching that undertaking, I think it would be strange if they did," he continued.
US Secretary of State Condoleezza Rice has said suspects are flown abroad for interrogation but denies torture is used.
But Conservative foreign secretary William Hague said claims about the flights and mistreatment of prisoners at Guantanamo Bay had undermined the struggle against terrorism.
Lib Dem acting leader Sir Menzies Campbell said the MPs' report made the government's "see no evil" approach to the flights claims "unsustainable".
The MPs' report also raised concerns about government attempts to sign agreements so they can return foreign suspects to their countries of origin without fear they will be tortured.
The MPs warned these "memoranda of understanding" should only be used once ministers are sure they can monitor whether they are working.
The agreements "must not be used as a fig leaf to disguise the real risk of torture for deported terrorism suspects", they say.
A separate report from Amnesty International condemned the attempts to agree the memorandums as "a dangerous circumvention of international law".
Mr Blair rejected the fears, saying: "We have got the whole thing upside down."
He wanted to ensure there were assurances that people deported would not be tortured.
But he added: "We cannot have a situation where people are just allowed to do whatever they want and we have just got to keep them here in this country and cannot return them."