The Guardian splashed this morning on the revelation that Tony Blair was aware of the ­existence of a secret interrogation policy which ­effectively led to British citizens, and others, being ­tortured during ­counter-terrorism investigations:

The policy, devised in the aftermath of the September 11 attacks, offered ­guidance to MI5 and MI6 officers ­questioning detainees in Afghanistan whom they knew were being mistreated by the US military.

British intelligence officers were given written instructions that they could not “be seen to condone” torture and that they must not “engage in any activity yourself that involves inhumane or degrading treatment of prisoners”.

But they were also told they were not under any obligation to intervene to prevent detainees from being mistreated.

“Given that they are not within our ­custody or control, the law does not require you to intervene to prevent this,” the policy said.

The policy almost certainly breaches international human rights law, according to Philippe Sands QC, one of the world’s leading experts in the field, because it takes no account of Britain’s obligations to avoid complicity in torture under the UN convention against torture. Despite this, the secret policy went on to underpin British intelligence’s ­relationships with a number of foreign intelligence agencies which had become the UK’s allies in the “war against terror”.

Lib Dem shadow foreign secretary Ed Davey has issued a press release today urging Mr Blair either to make clear the allegations are factually wrong, or to quit his current role as Middle East peace envoy:

Surely Tony Blair cannot hold the position of Middle East Envoy when he stands accused of breaking the UN Convention against torture. He needs to either make clear what he knew about the torture policy or stand down as envoy. He cannot have it both ways.

“There are also serious questions to answer for both Jack Straw and David Blunkett. They had oversight of MI6 and MI5 at the time, and should have known about any guidance their agents had been given.

“Parliament must be allowed a debate on the issue of oversight of guidance on interrogation and the current Justice Secretary, given his long-term involvement in this issue, should respond for the Government.”