Here's a way to get the much needed judicial public inquiry.
The opposition bands together, and yes forms a coalition, and takes down the government.
They announce their intention to setup an inquiry to investigate the potential torture of prisoners in Afghanistan. They will only stay in power long enough to get the inquiry going, hand over all necessary documentation and ensure the inquiry cannot be blocked or stymied by the efforts of the Conservative party.
After which they will dissolve the coalition and call a general election. The odds are strong that the public will punish the opposition parties for doing this, and return a majority Conservative government. It is a high price to pay.
I for one, think its worth it. If adherence to international and domestic law is to mean anything, this investigation needs to go forward.