The Attorney-General, Sir Patrick Mayhew, is to be questioned in the Commons about a decision by the Crown Prosecution Service to block a police inquiry into allegations of a cover-up of a "dirty tricks" campaign in Northern Ireland.
Tam Dalyell, Labour MP for Linlithgow, said yesterday he intends to raise the issue when Parliament returns after the Easter recess.
Sir Allan Green, QC the Director of Public Prosecutions, told Scotland Yard this week not to investigate allegations that the Ministry of Defence and the security service conspired to prevent Colin Wallace, a former army information officer, being given a fair hearing before the Civil Service Appeal Board in 1975.
Mr Wallace says he was forced to resign after complaining about a campaign to smear leading politicians and to cover-up child abuse at the Kincora boys' home in east Belfast.
David Calcutt, QC, who was asked by the Government to conduct an independent inquiry into the appeal hearings, discovered that "representatives of the Ministry of Defence" secretly approached the board.
Mr Calcutt said that those approaches should not have taken place and probably affected the outcome of Mr Wallace's appeal. He also said that Mr Wallace's secret job description in Northern Ireland was hidden from the board in a way that prevented it from adjudicating justly.
It is now believed that Mr Calcutt himself was not given the full details of this job description during his inquiry.
Scotland Yard detectives told James Nichol, Mr Wallace's lawyer, that the affair merited a police investigation, but added that they did not want to embark on an investigation if the DPP had no intention of bringing charges.
Yesterday Mr Nichol said he was amazed by Sir Allan's decision. "There may be lots of reasons why the DPP may not want to prosecute, but to say no to an investigation into what is a prima facie case of a criminal offence is quite staggering." he said.