Human rights groups and campaigning lawyers will not take part in an inquiry into what British security services knew about the alleged torture of terrorism suspects on foreign soil because it risks becoming a "whitewash," they said on Thursday.

The independent inquiry, announced by Prime Minister David Cameron in July last year, will examine allegations made by several Britons of Pakistani descent that they were abused in custody in Pakistan with complicity from British officials.

It will also look at allegations of mistreatment of those held at the U.S. prison at Guantanamo Bay, Cuba.

British authorities say they would never use, or encourage others to use, torture to obtain information and Cameron said it was important that the inquiry cleared up any questions of wrongdoing and restored Britain's moral standing.

In a letter to the inquiry, headed by senior judge Peter Gibson, 10 groups including Amnesty International, Reprieve and Liberty said they were disappointed that a decision on what material could be publicly disclosed would not be determined independently of government.

They added there would also be no meaningful involvement of former and current detainees, and so concluded they would not submit any evidence and attend any further meetings.

"Since the torture inquiry was announced a year ago, we have tried repeatedly to make it work," said Reprieve investigator Tim Cooke-Hurle.

"It is frustrating that the government has instead chosen to proceed with a secretive and toothless review. By ignoring the concerns of torture victims and major human rights organisations, the government risks a whitewash."

Cameron had said that intelligence material and any testimony given by security service officers would remain secret. The campaigners said this had been interpreted widely by the inquiry to mean that anything U.S. officials would find embarrassing would not be made public.

Early last year the previous Labour government lost a legal battle to prevent the disclosure of U.S. intelligence material relating to allegations of abuse by CIA agents.

Judges disclosed information given to Britain's domestic spy agency by the CIA that Binyam Mohamed, an Ethiopian citizen and British resident who was fighting to prove he was tortured and that Britain knew about it, had been mistreated in U.S. custody.

Cameron had said there were doubts about whether Britain's spies still had the trust of their allies.