By Colin Brown and Andrew Buncombe in The Independent

Pressure is mounting on the White House to answer claims that the CIA is using UK airports to fly terrorist suspects for torture in secret prisons in Europe. Elizabeth Wilmshurst, the former Foreign Office lawyer who resigned over the Iraq war, warned Tony Blair last night that he cannot duck the questions crowding in about the flights which could mean Britain has been complicit in torture.

In The Independent, Ms Wilmshurst, now a fellow of Chatham House, said the Prime Minister could not justify breaking the international convention against torture by saying the “rules of the game have changed” because of the war on terrorism.

Britain’s European partners stepped up the pressure for details to be disclosed about hundreds of secret flights by CIA-operated jets.

Sarah Ludford, a British member of the European Parliament’s civil liberties committee, said: “I am not at all reassured that there is sufficient determination by [member states] to establish the truth,” she said. “The allegations are now beyond speculation. We now have sufficient evidence involving CIA flights. We need to know who was on those flights, where they went.”

EU leaders are ready to follow up their request to Jack Straw, the Foreign Secretary, to challenge the White House. On Tuesday he wrote to Condoleezza Rice, the US Secretary of State, calling for details of the secret flights to be revealed. Mr Straw said yesterday he had raised the issue with Ms Rice. She is likely to face direct challenges about flights when she visits Brussels next week.

This month, prisoners were reported held in two eastern European countries, believed to be Romania and Poland, brought there on flights the CIA calls “extraordinary rendition”. Michael Ratner, director of the New York-based Centre for Constitutional Rights, said: “It’s a secret. No one knows what happens in the rendition process or in the gulag of secret CIA hellholes.”

But journalists and campaigners have tracked some of what is happening by monitoring the flight records of planes known to be used by the CIA. Plane-spotters have helped compile information on the aircraft – including one Gulfstream originally identified as N379P but now renumbered N44982 – and their movements.

Twenty-six planes apparently used by the CIA have made 307 flights in Europe since 9/11. Of these, 94 had stops in Germany and 76 in Britain, at Luton, Glasgow, Prestwick and Northolt. The UK government has denied prisoners are being held on a US-operated base on British-owned Diego Garcia.

John Sifton, a researcher for Human Rights Watch, which has released a list of 26 “ghost detainees” held by the US without access to lawyers, said probably only a few of the 307 flights involved moving prisoners. Most, he said, were likely transferring CIA personnel. “It’s impossible to know for sure how many are innocent,” he said.

There is a debate in the US about whether torture should be permitted for extracting information. A Bill tabled by Senator John McCain to outlaw torture passed the Senate but is being opposed by Vice President Dick Cheney, who wants special exemption for CIA agents.

Increasingly, politicians in Britain and Europe are showing a determination to find out whether the US has “black sites” in eastern Europe where harsh treatment of suspected terrorists would raise fewer questions. Alexander Alvaro, a German Liberal MEP and member of the European civil liberties committee, said Angela Merkel, the Chancellor, would raise the issue in talks with George Bush. “I think our Chancellor will point out that Germany would not tolerate secret camps in Europe.”

There are growing calls at Westminster for Mr Blair to block the CIA flights. The Labour MP Harry Cohen said: “It is not for the UK Government to connive in and facilitate people disappearance. The Government’s blind-eye approach to enforcing the law is not acceptable.”

An all-party group to challenge the UK and US Governments over the transport of suspected terrorists, was launched yesterday at Westminster. It will be chaired by Conservative MP Andrew Tyrie, former Labour foreign affairs minister, Chris Mullin, and Sir Menzies Campbell, the deputy leader of the Liberal Democrats.