British officials have found no evidence that America is using UK airports to move CIA terror suspects, Foreign Secretary Jack Straw has said.
Reports of 210 CIA flights since 9/11
Mr Straw said no records of requests, nor any other files on the issue, had been found in detailed searches.
Campaign group Liberty wants police to examine whether suspects go through the UK to places where they face torture.
Lib Dem Sir Menzies Campbell said the fact there were no records did not mean the flights were not happening.
"I'm pretty certain it's not enough for the government to have a kind of 'hear no evil, see no evil' policy," said Sir Menzies.
The Guardian newspaper claimed in September that at least 210 CIA flights had landed in the UK since the 11 September 2001 US terror attacks.
Mr Straw told BBC Radio 4's Today programme: "Careful research has been unable to identify any occasion... when we have received a request for permission by the United States for a rendition through the United Kingdom territory or airspace.
"Nor are we aware by other means of any such case. Our people have checked through all the detail of the Liberty suggestions.
"They have found no records which corroborate either the details of what Liberty say and no papers relating to any policy considerations of what Liberty say."
Mr Straw was asked if he was saying he did not believe that any CIA flights carrying suspected terrorists had touched down in the UK en route to another country where they might be tortured.
"That appears to be the case," said Mr Straw. "Now you are asking me to prove a negative."
He said it was the practice of the US government to ask permission of the UK when it has sought such transfers in the past.
Two such requests had been approved for flights taking suspects to the US for trial in 1998, under the Clinton administration, he said.
Legal action threatened
But another, where a suspect was being taken to a third country, had been refused by Mr Straw because he was "not satisfied" about the circumstances.
"We have checked the records as carefully as we can and I believe the answer we have given from the records suggest that there have been no such flights through United Kingdom territory," he said.
"We will continue to look at the evidence that Liberty and others have provided and to carry on making those checks."
The foreign secretary said he was giving the information in response to a parliamentary question tabled by Sir Menzies.
But Sir Menzies said the issue would "run and run".
A system for inspecting flights was needed, he said, and the UK had a "moral responsibility".
Human rights group Liberty has threatened to sue the UK government if it fails to act.
Human rights groups in Scotland have warned airport staff they could face prosecution if they have anything to do with US flights allegedly taking terror suspects to be tortured.
Responding to Mr Straw's comments Sir Menzies Campbell said: "I have no doubt of the good faith of the foreign secretary in this matter but the truth is that the British authorities simply don't know whether extraordinary rendition is taking place using British airfields."
Tony Blair has said it is vital to distinguish between taking a suspect from one country to another and torture.
At prime minister's questions on 7 December, he defended co-operation with the US over the transfer of terrorism suspects and said "international conventions" had to be applied.
US Secretary of State Condoleezza Rice has admitted terror suspects are flown aboard for interrogation, but denies they are tortured.
She said suspects were moved by plane, and it was under a process known as rendition which was a "lawful weapon".