The government is unaware of any cases of the US moving terror suspects through the UK that it has not already told MPs about, Jack Straw has said.
Mr Straw is under pressure to explain UK involvement
The foreign secretary was forced to issue a written statement after a leaked memo said more "extraordinary rendition" cases were on file.
The US is accused of flying suspects to countries where they could be tortured.
The Foreign Office memo warned ministers such operations were almost certainly illegal.
In his statement, Mr Straw said he had already given MPs all the information he had about US requests to use British airspace or airport facilities for "extraordinary rendition".
"We have found no evidence of detainees being rendered through the UK or overseas territory since 11 September 2001," said Mr Straw.
"We have found no evidence of detainees being rendered through the UK or overseas territory since 1997 where there were substantial grounds to believe there was a real risk of torture."
He said there were four cases in 1998, when the US requested permission to render one or more detainees through the UK, two of which were denied.
That is one more case than three the government had previously confirmed.
Mr Straw said he had told Washington he would expect it to seek permission before flying detainees through the UK.
"We will grant permission only if we are satisfied that the rendition would accord with UK law and our international obligations, and how we understand our obligations under the UN Convention Against Torture."
He added: "We are also clear that the US would not render a detainee through UK territory or airspace (including overseas territory) without our permission."
The government has faced calls from some MPs to ban US rendition flights from UK airspace amid concerns about torture.
The Foreign Office memo, leaked to the New Statesman, warned rendition was illegal under both UK and international law, except in certain rare, "tightly defined" cases - and that co-operating with US rendition operations could also be unlawful.
Any case where there was a "real risk" of torture could never be legal, it said.
It advised ministers questioned on the issue to refer to comments by US Secretary of State Condoleezza Rice, who said the US did not transport people to countries when it believed they would be tortured.
But the memo also revealed a difference of opinion over what constitutes torture in law, suggesting the US authorities applied a less rigorous definition of "cruel, inhumane or degrading treatment" than the United Nations Convention Against Torture.
The document also said there was "no mechanism" for establishing whether suspects captured by British forces in Iraq or Afghanistan had subsequently been transferred by the US to interrogation centres.
Shadow foreign secretary William Hague, who wrote to Mr Straw demanding a statement, said he wanted to know if the foreign secretary was "entirely satisfied that UK airspace and territory has not been used for the transfer of suspects leading to their torture".
Liberal Democrat foreign affairs spokesman Nick Clegg said: "Today's statement adds nothing to what we already know and begs the question why the government have been so reliant on Condoleeza Rice's statement given that the US definition of torture appears narrower than the UK's."
Liberal Democrat calls for a full public inquiry into alleged UK complicity in "extraordinary rendition" were rejected on Thursday by Commons leader Geoff Hoon.