Precedent of a dangerous kind is at risk of being set in Scots law. As The Herald reveals today, the Crown Office will ask judges to replace the defence team representing Abdelbaset Ali Mohmed al Megrahi with security-vetted special advocates for the court hearing next week to decide whether a document thought to contain vital information about the timer that detonated the Lockerbie bomb should be made public. The Scottish Criminal Cases Review Commission concluded that failure to disclose the document during the original trial could constitute a miscarriage of justice.

This is a key component in the appeal against al Megrahi's conviction. However, the Crown has refused to disclose the document to al Megrahi's defence team on grounds of national security (the position also of the UK Government). The scene was set for a battle royal between defence and prosecution in the Court of Criminal Appeal next Tuesday. However, should the Crown hold sway, the outcome will be viewed as putting the defence at a distinct disadvantage, calling into question whether the right to a fair trial had been seriously undermined.

It would serve the interest of justice better if the defence team were to put their case to the appeal court judges. Special advocates operate in criminal cases in England under the auspices of Public Interest Immunity (PII) hearings, which arbitrate on whether sensitive information which could compromise security or otherwise be against the public interest should be disclosed. PII hearings are not yet in place in Scotland and it is not known if there is a list of Scottish special advocates who could represent al Megrahi in the defence team's absence. If there is such a list, it would be approved by the Lord Advocate, who heads the Crown Office - the very agency that does not want the document disclosed. That is not guaranteed to reassure in the context of the paramountcy of a fair trial.

The Lockerbie appeal is a complex matter and, regardless of where the special advocates came from, they would be unaware of the intricacies of the case. The defence team could not brief them on advancing the appeal as its members do not know what is in the document at the heart of the dispute. Special advocates could not brief the defence team as the terms of their involvement would ban them from doing so. It would a highly unsatisfactory scenario.

In principle, PII hearings provide a forum for testing and balancing conflicting interests. To enjoy public confidence, they must allow a challenge to withhold information on public interest grounds to be advanced on robust grounds. If a challenge were to be mounted by special advocates in the appeal court next week it would not be robust or enjoy public confidence. This appeal comes in the wake of the damning judicial criticism of the Blair government and the Serious Fraud Office for dropping the criminal investigation into the Saudi arms deal on grounds (unwarranted, as it turned out) of national security. The same argument has been put forward by the Westminster government to justify keeping the Lockerbie document under wraps. That justification should be the subject of a robust challenge on the part of al Megrahi's defence team. Nothing less will satisfy justice.