Campaigners have repeated the call that the Crown should not consider a police report into criminal allegations over the Lockerbie investigation.

Police Scotland has revealed that it is close to ending a three-year probe in to nine allegations of criminality against the prosecutors, police and forensic officials involved in the case.

Only one man has ever been convicted in connection with the 1988 bombing in which 270 people died, Abdelbaset al-Megrahi.

Campaigners who believe Mr Megrahi was wrongly convicted argue the police report should not be handed to the Lord Advocate and Crown Office, but to an independent prosecutor instead to consider what, if any, action should be taken. The Lord Advocate, however, has said he will play not part in reviewing the evidence and has appointed an independent QC to do so.

As The Herald revealed yesterday, Police Scotland has also asked an independent QC to review its report rather than rely on guidance from the Crown.

However, the Justice for Megrahi group, which includes prominent lawyers, believes this is not enough.

Brian McConnachie QC, speaking ahead of an Edinburgh conference on Wednesday, said: "Having declared the allegations to be defamatory, unfounded, false and misleading, it is in my opinion impossible for any decision of the Lord Advocate arising out of the allegations to be seen to be impartial, objective or unbiased."

Fellow campaigner Partick Harvie of the Scottish Greens said: "While the Lord Advocate rightly enjoys independence and freedom from political influence when considering police reports into criminal acts, that consideration must be seen to be truly independent and not coloured by any bias or prejudice whatsoever."

A Crown spokesman said: "The Lord Advocate has repeatedly made it clear that he has no involvement in dealing with the allegations nor will he have any involvement.

"Arrangements have been put in place to ensure any prosecutorial function in relation to this matter is dealt with by independent counsel who has had no involvement in the Lockerbie investigation."

The Crown insists that Lockerbie remains a live investigation and is understood to be pursuing other Libyan officials it believes may have been responsible for the atrocity.

Megrahi died in Libya in 2012 having been released from a Scottish jail in 2009. He always insisted on his innocence. The North African country is currently in chaos with UK troops to be deployed to support its weak military.

The Pan Am flight was on its way from London to New York when it exploded above Lockerbie on the evening of December 21 1988, killing everyone on board and 11 people on the ground.