The Crown Office yesterday launched a legal bid to limit the scope of the Lockerbie bomber's appeal.

In what is regarded as an unprecedented move, prosecutors said the grounds of Abdelbaset Ali Mohmed al Megrahi's appeal should be confined to the six terms of referral made by the Scottish Criminal Cases Review Commission (SCCRC) in its report last summer.

It said that any extra grounds of appeal would require the court to exercise its discretion in allowing them.

Yesterday, Crown counsel Ronnie Clancy QC opened proceedings by arguing the defence's position was not competent in law, and branded it "absurd" and "illogical".

However, lawyers acting for Megrahi, the Libyan convicted of the bombing, say the appeal should include all the points pertinent to the case, including new evidence not seen by the commission.

The defence has already made it clear that the scope of appeals in Scotland are not ordinarily restricted to the reference of the commission.

In fact, judges rejected a similar move in 2004 to restrict the appeal of TC Campbell and Joe Steele, whose appeal against conviction for the Ice Cream War killings was upheld.

Megrahi, 56, is currently serving a 27-year sentence in Greenock after being found guilty in 2001 of bombing PanAm Flight 103. He lost an appeal in 2002, but last year the SCCRC, an independent body set up to investigate alleged miscarriages of justice, referred his case back to the appeal court.

At the special five-judge hearing, Mr Clancy said the circumstances of the case were "truly exceptional" given the volume of material. The SCCRC looked at a transcript of the lengthy trial, 15,000 statements, and a substantial amount of material produced by his lawyers.

Mr Clancy said it also obtained additional material from police, Crown Office, and other agencies. Inquiries were undertaken in Britain, Malta, Libya, and Italy and numerous witnesses were interviewed independently by them.

"The Crown of course accepts that the appellant has a competent appeal by virtue of the commission reference in this case," said the advocate depute.

But he added that what was in dispute was the prosecution contention that it should be confined to grounds of appeal centred on or giving reasons for the SCCRC referrence. Anything else, he claimed, would require the court to exercise its discretion to allow additional grounds.

He said that it was now asserted by Megrahi that the commission never intended to carry out "an exhaustive analysis of the case".

The hearing to decide the ultimate scope of Megrahi's appeal is being heard by Scotland's most senior judge, Lord Hamilton, the Lord Justice General, sitting with Lord Kingarth, Lord Eassie, Lord Wheatley, and Lady Paton.

The hearing continues today.