MPs and human rights group have accused ministers of a cover-up over government knowledge of rendition flights and the use of British military bases to hold suspects after the United States launched its war on terror more than six years ago.

Now ministers have blocked an attempt by an influential parliamentary committee to secure the release of secret military papers which they believe will reveal whether the British island territory of Diego Garcia was used as a detention centre for rendition prisoners.

MPs from the All-Party Parliamentary Group on Extraordinary Rendition used powers under the Freedom of Information Act to request minutes of US/UK political military talks held in a Washington in September last year.

Download the new Independent Premium app Sharing the full story, not just the headlines

But the Government has refused to release the papers claiming that to do so "would prejudice the defence" of territory by "exposing plans to counter possible terrorist attacks". They also say it could damage diplomatic relations between Britain and America.

The Parliamentary Group chairman, Andrew Tyrie MP, says this is another example of government obfuscation in his committee's attempt to get to the truth about the use of state-sanctioned kidnapping on the British island. He has launched an appeal against the Foreign Office decision not to release the Diego Garcia documents.

"Cover-up and obfuscation by the UK government have hampered efforts to discover the truth about British involvement in the US rendition programme from day one," he says. "There have been repeated allegations that the US has used the British territory of Diego Garcia in its rendition programme. Yet the Government has done next to nothing to investigate them, and continues to rely on US assurances which have been called into question by the Intelligence and Security Committee."

The Government has been careful to say as little as possible about what it does or doesn't know about US "ghost flights" in which suspects are flown from secret prisons to third party state detention centres. In the past it has relied on US assurances that no British territory loaned to the Americans has or is being used to facilitate this illegal activity.

But the UK human rights charity Reprieve has uncovered credible evidence which it believes casts doubt on these assurances. In its report on rendition published last year it says that Diego Garcia has been the subject of repeated, credible and concurrent claims that the island has played a major role in the US system of renditions and secret detention.

Reprieve submits that the UK's failure to conduct a prompt, independent and effective inquiry into these claims is a further clear breach of its duties under international and domestic law.

"Unlike the treatment of our clients who were apparently held there without charges or trial, we are very glad for the UK government to have a fair hearing before standing condemned of complicity in kidnapping and abuse of prisoners," says Clive Stafford Smith, Director of Reprieve. "But they cannot simply refuse to hold a public hearing at all and expect us to believe their denials, when senior US officials have more than once admitted that Diego Garcia has been used in the illegal rendition programme."

"It is the policy of extraordinary rendition which damages the public interest, not allowing the truth to be told about it," says Mr Tyrie. "That is why I am appealing against this decision, and will continue to do what I can to uncover the truth about rendition and Diego Garcia."

In a separate move, the MPs have written to an American general asking him to give evidence about rendition on the Indian Ocean island. General Barry McCaffrey has twice claimed in interviews with the media that detainees are being held by the US military on the island.

r.verkaik@independent.co.uk