Allegations of impropriety by the Crown Office which have come to light in respect of the Abdelbaset Ali Mohmed Al Megrahi case can only be investigated by the Inspectorate of Prosecutions if they are directed to do so by the head of the Crown Office against whom the allegations have been made.

The conundrum has come to light after Christine Grahame MSP asked the Justice Minister to confirm whether Crown Office "impropriety" regarding the alleged non-dislcosure of material evidence in the Megrahi case could be investigated by the Inspectorate.

In response, MacAskill revealed that the Inspectorate requires to have a referral made to it by the Lord Advocate, to whom the subsequent report is also addressed for action.

"Under the Criminal Proceedings etc (Reform) (Scotland) Act 2007, the Chief Inspector of Prosecution in Scotland is required to submit to the Lord Advocate a report on any particular matter connected with the operation of the Service which the Lord Advocate refers to the Inspector," MacAskill said.

"The Scottish Government has no power to direct the Inspectorate of Prosecutions to establish an inquiry on any matter."

The Inspectorate's Chief Inspector, Joseph T O'Donnell, joined the Procurator Fiscal Service in 1975, working in the Crown Office Policy Unit and was Senior Assistant Fiscal at Glasgow prior to taking up his post.