In a statement yesterday, Police Service of Northern Ireland chief constable Jon Boutcher said it was “unacceptable that MI5 continue to provide material to the Operation Kenova team so long after they undertook to have given full access to Kenova of all the material they held about the agent Stakeknife”.

Hundreds of pages of documents are understood have been supplied by MI5 following the completion of the review, which informed a decision by Northern Ireland prosecutors not to bring charges against 16 suspects.

Mr Boutcher said: “My interim report highlighted a number of issues in obtaining information from MI5 and I reported the similar experiences of Lord Stevens, Judge Cory and others who each called out the unacceptable practices of those not co-operating with and withholding information from legacy investigations.

“The fact that this information continues to be provided to the Operation Kenova team after the Public Prosecution Service have directed on the files submitted to them will cause further upset to the families who had already waited many years to find out what happened to their loved ones.”

He added: “I am confident that the officer in charge of Operation Kenova, Sir Iain Livingstone, will ensure all the material is fully assessed and will liaise closely with the director of the Public Prosecution Service to determine if any further direction is necessary.

“I very much look forward to his final report that will comment more fully on these most recent disclosures.

“I have a huge respect for our intelligence agencies as they work tirelessly to keep society safe however, I remain concerned that where matters relating to Northern Ireland’s legacy are involved there continues to be an unhelpful protectionist approach to disclosure.

“This results in wild conspiracy theories and inaccurate reporting about legacy cases.”