Image caption BBC Spotlight obtained a secret recording of a police officer working for Operation Kenova

New secrets related to the Northern Ireland Troubles have been uncovered within MI5.

The documents were previously withheld from official inquiries, such as those conducted by Lord Stevens into state collusion with loyalist paramilitaries.

They were uncovered during Operation Kenova - the recent police investigation into the agent within the IRA known as Stakeknife.

Officers are said to have found a new document "every couple of weeks".

Stakeknife is alleged to have been west Belfast man Freddie Scappaticci, who was supplying the Army with top-level intelligence on the IRA for two decades.

He has denied being the informer.

BBC Spotlight obtained a secret recording made last year of an English police officer working for Operation Kenova.

Image copyright Pacemaker Image caption Fred Scappaticci strenuously denies he was an Army agent within the IRA

In it, he said that documents which had been found were "very telling".

He added MI5 had retained material "they probably should have got rid of".

A file on the activities of Stakeknife has been completed for the Director of Public Prosecutions, who will decide if there is enough evidence to bring any charges.

The agent has been implicated in dozens of murders.

The man heading Operation Kenova, the retired chief constable of Bedfordshire Jon Boutcher, has previously stated the investigation could result in charges against former members of the IRA, the Army and MI5.