Tony Blair is facing calls for a public inquiry into America's use of UK airports to transport terror suspects.
The leaked memo has reignited the row over the flights
The Liberal Democrats accused ministers of "crude" spin after a leaked memo advising them how to avoid questions on the subject from MPs was revealed.
But Commons leader Geoff Hoon told MPs the government had since provided the full facts and had nothing to hide.
The US has been accused of flying suspects to secret detention centres where they could face torture.
The memo from December last year referred to two US flight requests which had been uncovered by officials, from 1998, but said there "could be more". A further request has since been uncovered.
Rejecting calls for a full public inquiry into alleged UK complicity in the "rendition" of terror suspects, Mr Hoon told MPs Foreign Secretary Jack Straw had already given all the facts.
Under the UN Convention Against Torture, it is illegal for Britain to allow the US to use its airspace where there is a real risk a prisoner will be tortured.
Mr Straw has said the UK would never allow this to happen, citing assurances from US Secretary of State Condoleeza Rice that her country does not condone the use of torture.
But the memo at the centre of the row reveals a potential difference of opinion over what constitutes torture - and concern among Whitehall officials that US activities may be illegal under international law.
The December 2005 document also suggests ministers knew little about how many UK airports had been used, advising them to avoid detailed questions and stress the anti-terror purpose of the practice.
"It does remain true that we are not aware of the use of UK territory or airspace for the purposes of extraordinary rendition," the memo says.
"But we think we should now try to move the debate on and focus people instead on [US Secretary of State Condoleezza] Rice's clear assurance that US activities are consistent with their domestic and international obligations and never include the use of torture."
The memo also suggests people captured by British forces in Iraq or Afghanistan could have been sent to potentially illegal interrogation centres.
Downing Street attempted to draw a line under the row on Thursday saying Mr Straw had detailed all known rendition requests since 1997 since the memo was written.
"This is a classic case where people have got over excited by getting a leaked memo, rather than actually reading the content of it," the prime minister's official spokesman said.
According to statements made by Mr Straw to MPs, the UK has not received a single rendition request from the Bush administration and just three during Bill Clinton's time in the Whitehouse.
But shadow Foreign Secretary William Hague said he would be writing to the Foreign Secretary to demand answers to key questions.
"Are the government satisfied that people have not been rendered through UK territory and airspace in recent years in a way which may lead to their torture?," he asked.
Liberal Democrat acting leader Sir Menzies Campbell said he would be writing to Mr Blair to demand a full statement.
"This memo appears to suggest that at least somewhere in the government someone was giving advice to Number 10 Downing Street that rendition was probably illegal, that there was probably an obligation to make investigations," he told BBC Radio 4's Today programme.
Meanwhile, MEPs have launched their own investigation into US rendition flights. It comes in addition to 10 or more separate inquiries taking place in individual European states.