The government is being urged to take action over claims that UK airports are being used by the CIA to transport suspects to countries where they might be tortured.
Human rights group Liberty has warned that Britain could be in breach of domestic and international law if it was found to have allowed the so-called 'extraordinary rendition' flights to land and re-fuel in Britain.
However, the Foreign Office has denied any knowledge of the flights, and insists it has not received requests nor granted permission for such activities.
Reports suggest the US secret intelligence agency has a number of secret camps where it is holding terrorist suspects, and speculation is growing that flights carrying these suspects may have landed in European airports to refuel.
The White House has neither denied nor confirmed the allegations, which first appeared in US media, although several EU member states have already begun investigations.
Foreign secretary Jack Straw yesterday wrote to Washington on behalf of the EU to seek clarification on the reports, but Liberty director Shami Chakrabarti today called on Mr Straw to seek assurances within a fortnight that British airports are not being used for this purpose.
"It is troubling that our government chases Algeria for anti-torture assurances but cowers from confronting the USA on the same issue," she said.
"It is the abhorrence of torture that distinguishes all democrats from dictators and terrorists. What can we say to those who perpetrate atrocities in London and around the world if we allow ourselves to become complicit in the cheapening of human life?"
Liberty has also called on regional police chiefs to investigate any extraordinary flights at their local airports, urging them to report back within the same two-week period.
Liberal Democrat foreign affairs spokesman Menzies Campbell welcomed the campaign group's call, saying that "at long last", the issue was getting the attention it deserved.
"The transfer of individuals from one jurisdiction to another so that they can be treated more harshly is both immoral and illegal," he said.