Full disclosure: If Britain was involved in the torture of those imprisoned by the US we need to be told

Publication this week of the US Senate report into the activities of the CIA following 9/11 will not end the debate about the effectiveness and appropriateness of the agency’s interrogation methods.

The bitter wrangling of recent days is clear evidence of that, with the key figures of the Bush/Cheney era battling desperately to save their legacy.

Yet considering the past strength of public support in America for the “war on terror” – and for the use of harsh measures by intelligence agencies where necessary – the mere fact of the Senate’s investigation is notable. In a poll five years ago, only a quarter of Americans believed the use of torture could never be justified. Now that so much doubt has been cast on the efficacy of what are euphemistically termed “enhanced interrogation methods”, public opinion in the United States will surely change.

The conclusions of the Senate Intelligence Committee remain only partially available to the public, and it was inevitable perhaps that some elements would stay classified. Nevertheless, the work of the Committee has been conducted and completed in a way that is hugely impressive. By contrast, the UK authorities continue to dally. In the light of what we know as a result of the American inquiry, there can be no justification for that.

Confirmation yesterday that UK intelligence agencies spoke to their US counterparts to discuss redactions to the Senate report only increases the sense that the public needs to be reassured about what activities were undertaken in the name of British security. Similarly, the suggestion that intelligence operatives in this country may have used evidence obtained by the mistreatment in detention of Moazzam Begg needs further explanation.

Indeed, the case of Mr Begg is emblematic of the tangled relationship between British and American security agencies. After all, Mr Begg was known to MI5 and Special Branch as long ago as the late 1990s; then came his detention in Afghanistan and subsequent transfer to Guantanamo Bay; and on his release and return to Britain he again found himself the subject of inquiries by counter-terrorism officers. Co-operation and co-ordination between UK and US intelligence services is important. But the British public has the right to know how the association has worked. In particular, it has a right to know the full extent to which the authorities in this country were complicit in mistreatment of prisoners.

As things stand, it seems as if the investigation which David Cameron asked Parliament’s Intelligence and Security Committee this year to complete will not start taking witness statements until the general election has been and gone. That inquiry is itself picking up from where the stalled investigation by Sir Peter Gibson left off at the end of 2013. Nick Clegg says he is keeping an open mind about a possible judicial inquiry in the future.

None of this sounds very urgent, and yet the question of how much those in power here knew about the CIA’s methods is crucial, not least at a time when disenchantment with the governing class is already considerable. Perhaps this is the rub. After all, any examination of the role of MI5 and other relevant agencies cannot be the end point for Parliament’s inquiry. The part played by ministers too will have to be properly assessed.

Just as that process is proving challenging for George W Bush and Dick Cheney now, so it might be uncomfortable for the likes of David Miliband, Jack Straw and Tony Blair in the months to come.