The parliamentary panel investigating allegations of British involvement in torture is seeking access to secret parts of an damning US report into CIA tactics in the wake of the 9/11 attacks in 2001, its head has confirmed.
Intelligence and Security Committee (ISC) chair Sir Malcolm Rifkind said it would request sight of any redacted sections of the Senate Intelligence Committee's findings related to the UK's role in the rendition and interrogation of terror suspects.
"What needs to be discovered is whether they were aware of what the CIA was doing; whether they were willing to accept intelligence obtained by waterboarding and other inhumane practices, and whether they volunteered questions to be put to detainees being interrogated by the CIA," Sir Malcolm said.
Downing Street has confirmed that British spies spoke to their US counterparts to discuss blacking out some sections but insisted it related only to "national security grounds" and not to cover-up British complicity in torture.
Former home secretary Alan Johnson said Jack Straw and Tony Blair should go before the committee.
Speaking on The Andrew Marr Show, he added: "It is right the Intelligence and Security Committee see what was redacted so they can be sure this was to protect sources, British agents in the field.
"I'm absolutely convinced that what was redacted was what the Home Office says they wanted redacted."
Straw told the Telegraph: "I was never complicit in any of the CIA illegal processes. I consider it to be revolting, unlawful and also unproductive, as has come out in the Senate report.
"Of course, when it is possible for legal reasons for full inquiries to take place I will co-operate fully with them, as I always have done."
Sir Malcolm, interviewed on the same programme, said his committee would request any former minister or serving minister with a contribution to make to give evidence.
He added: "If they refuse to do so that in itself would imply they have something to hide. We will decide who in the intelligence agencies, who from the Government or former governments or anyone else needs to be subject to our evidence sessions.
"If there is evidence they knew or were involved then of course they would be priority figures for our investigation. If people deserve to be embarrassed it's our job to embarrass them.
"We have a statutory obligation to carry out this task without fear or favour and if our conclusions are that either serving ministers or former ministers or MI6 or MI5 or anyone else were complicit in torture we will say so and we will indicate the evidence that has brought us to that conclusion."
Shadow home secretary Yvette Cooper said she doubted the ISC "have the capacity and the scope" to carry out an inquiry and it remained her "instinct" that a judge-led process would still be required to ensure confidence.
Blair and other former ministers had "always said that they would co-operate with all investigations and have said that they would be very keen to do so," Cooper said.
It was important to get to the truth to make sure there was no "shadow of innuendo or allegations cast over the vital work that the agencies rightly do to keep us all safe every day of the week," she added.
Isabella Sankey, director of policy for Liberty, said: "Torture is torture - it's unjustifiable, no matter how many or how few people knew it was happening.
"Anyone, anywhere, who was complicit in these crimes must face prosecution but until our Government sets up a transparent, judicial inquiry, cover-up and official impunity will persist."
The revelation of 23 meetings between senior UK figures - ambassadors to Washington and the then security minister Admiral Lord West - and members of the Senate committee helped fuel demands for a full investigation.
Lord West, who was previously chief of defence intelligence, has acknowledged it was possible individual British spies in the field knew what US counterparts were doing to detainees but denied lobbying the committee over the issue.
Sir Malcolm said it was for the US Government to decide whether to supply his inquiry with redacted material rather than the committee.
"We are taking the steps that are normally taken to try to obtain information. There are various ways in which this might be dealt with."
Asked if he was hopeful of success, he said: "I do not say I would be confident."
The report also sparked calls for Britain to halt planned negotiations over America's continued use of Diego Garcia - part of the British Indian Ocean Territory - for a vast military base.
In 2008, it was revealed that the US had secretly used the island as part of its "extraordinary rendition" programme without informing British ministers - in contravention of previous assurances.
The present 50-year agreement allowing the US to use the island runs to 2016.
Andrew Tyrie, chair of the all-party parliamentary group on rendition, told The Observer: "The negotiations on the lease can focus minds on establishing the scope and limits of Britain's involvement, direct or indirect, in extraordinary rendition.
"We are talking about kidnap and taking people to places where they may be maltreated or tortured."
Liberal Democrat former Home Office minister Norman Baker said: "We need a full explanation of what happened in our name on that island."
Deputy Prime Minister Nick Clegg has acknowledged a full judicial inquiry may still be required into allegations of British complicity in torture if police and parliamentary probes fail to answer key questions.
The ISC was given responsibility for the probe after a judge-led examination was halted due to police investigations of rendition claims.
Writing in The Sunday Telegraph, Sir Malcolm confirmed that the ISC would examine the use of Diego Garcia "and whether the Government or the agencies have, in any way, tried to have redacted parts of the Senate report that might have been embarrassing".
Its work should be completed by the end of next year and the findings published "without fear or favour".
He sought to play down concerns that the ISC had sufficient teeth to investigate the claims of complicity after two previous reports on detainees and rendition turned out to be inaccurate because the intelligence agencies had not supplied all the relevant evidence.
"It cannot happen again," he insisted.
"At that time the ISC could only ask MI6 or MI5 to hand over their files. We had no legal power to force them to do so. They could choose what to show us. We insisted to the Government that the law had to be changed and that happened over a year ago.
"The intelligence agencies now have no choice. By law they must hand over any files and documents that we require. In addition, our staff now visit the headquarters of MI6, MI5 and GCHQ and can personally inspect any additional files that might be relevant to our inquiries."
Defence Secretary Michael Fallon said Tony Blair and Jack Straw should tell the ISC what they knew at the time as prime minister and foreign secretary.
"It's for ministers in that government to account for their actions," he told the Sunday Telegraph.
"That is our tradition and that's the expectation. I hope they will co-operate with any parliamentary inquiry."
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