Claims of NI 'collusion' between UK agents and paramilitaries
A BBC investigation has revealed claims that British security forces had thousands of agents and informants working inside paramilitary groups in Northern Ireland.
The undercover operatives were recruited by the army, MI5 and Special Branch, and many were allegedly involved in criminality and murder.
The government says collusion with paramilitaries should never have happened and that it has apologised where it did.
Chris Buckler reports.
Panorama: Britain's Secret Terror Deals is on BBC One at 2100 BST on Thursday 28 May 2015 and available later via BBC iPlayer.