UUP leader Doug Beattie has asked the Public Prosecution Service (PPS) when a decision will be made about files linked to the activities of the agent known as Stakeknife.
Around 30 files have been forwarded to the PPS by Operation Kenova, which was set up in 2016.
West Belfast man Freddie Scappaticci has been named as the agent who was a senior figure in the IRA's internal security unit, but has denied the allegation.
The investigation is being headed up by former Befordshire police chief constable Jon Boutcher.
Kenova's scope was later widened to include other high profile cases.
Mr Beattie last night said it was his understanding that the PPS "was due to take a decision regarding prosecutions by the Spring of 2022".
“Up to now there has been no public comment from the PPS regarding this case, and I have therefore written to the DPP (Director of Public Prosecutions) seeking confirmation that he has indeed received the files from the Operation Kenova team, and asking when a decision is likely to be made regarding these files," he said.
“I fully understand that this is a complicated process and the fact that the government’s legacy bill is progressing through parliament does not make matters any easier, but it is my belief that these files should be progressed as soon as possible and the decisions around them made public.”
A spokesman for the PPS said: “A number of files submitted by Operation Kenova concerning the alleged criminality of an agent known as Stakeknife remain under active consideration.
“Work is progressing as quickly as possible and decisions will issue in due course.
