The Government has stepped in to block access to a mystery document that could cast doubt over the conviction of the Lockerbie bomber.

The official papers have been requested by lawyers representing Abdelbaset Ali Mohmed Al Megrahi, who is appealing against his conviction for the 1988 atrocity.

But a court hearing today heard that the document, handed to prosecutors by an undisclosed foreign government, is likely to be subject to an order banning the disclosure of its contents to the public.

The Advocate General, the top UK law officer in Scotland, intends to lodge a Public Interest Immunity plea after the government in question refused to grant its disclosure.

Objecting to the move, Al Megrahi's lawyers said that only Scotland's top prosecutor, the Lord Advocate, has the authority to make that decision on behalf of the public.

Margaret Scott QC told judges at Edinburgh High Court: "When it comes to criminal proceedings, it's for the Lord Advocate to assert public interest."

But Crown Counsel Ronnie Clancy QC, defended the position, claiming it was an issue reserved for the UK Government.

"The view was taken by the Lord Advocate that the Public Interest Immunity should be left to the UK Government because the subject matter of the plea was likely to be a reserved matter."

Today's hearing, on the eve of the 19th anniversary of the bombing, took place after the Crown had previously pledged to resolve the matter of the document request.

Mr Clancy told an October hearing that there was "a distinct possibility" that some or all of the documents requested by the defence would be disclosed within six weeks.

But today the Crown asked further time to discuss the issues surrounding the document.

It is understood that a certificate must also be submitted to the court in relation to the Public Interest Immunity plea.

The request for extra time was granted by judges who criticised prosecutors over the delays and their failure to provide more thorough answers to the defence's requests at the last hearing.

The Lord Advocate was also rebuked.

The Lord Justice General, Lord Hamilton, said: "We regard it as very unsatisfactory that the Lord Advocate has not seen fit to make plain in her answers what her position is in relation to Public Interest Immunity."

Al Megrahi is serving a minimum of 27 years for the bombing, which occurred when the Pan Am flight 103 exploded over Lockerbie, killing 270 people.

The Scottish Criminal Case Review Commission (SCCRC) referred the case back to the court earlier this year after ruling that there were six grounds where they believed a miscarriage of justice may have occurred.

One of the grounds was the non-disclosure of documents by prosecutors at Al Megrahi's trial.

Defence lawyer Ms Scott said: "It's the Lord Advocate's duty to consider... whether or not a document should be disclosed to the defence to ensure a fair trial.

"I cannot understand why there is this almost 'hiding behind' the Advocate General."

The Advocate General Neil Davidson QC was in court for the hearing which lasted almost three hours.

Mr Davidson also requested further time to complete his answers on the documents to the court.

A debate on the Public Interest Immunity plea has been set for February 20.

Former Libyan intelligence agent Al Megrahi, who is being held in Greenock prison in Inverclyde, lost a previous appeal against his conviction in 2002.

The document setting out the grounds for the new appeal are to be lodged with the court tomorrow.

The Crown said it expected the grounds to go "well beyond" the point on which the case was referred back to the court by the SCCRC and sought to limit them to the Commission's findings.

Prosecutors also asked for restrictions on the defence's access to Crown productions.

They want Al Megrahi's lawyers to have access only to those directly related to specific grounds of appeal.

Ms Scott contested the request, saying the Crown had been "nothing but obstructive" in relation to accessing the productions.

Prosecutors were granted a month in which to launch any opposition to the scope of the appeal. The issue of productions will be discussed at a later date.

Jim Swire, whose daughter Flora died in the bombing, attended today's hearing.

Mr Swire, who believes Al Megrahi to be innocent, described today's proceedings as "worrying".

He said: "It's clear that the Lord Advocate had decided to divulge it (the document) to the SCCRC in the past and did not fight the SCCRC's request to see those documents.

"As a result of seeing it, the SCCRC said two things - that the content of one of the documents appears to contain material which might mean that the original trial was unfair, and that the Crown's failure to divulge the document to the defence in itself was another reason why the first trial might have been unfair.

"I think that the Crown has its back against the wall on this issue."

Mr Swire said of the Crown's attempt to limit the scope of the appeal: "That seems to me to fly in the face of what the court appeared to me to say last time, namely that the defence would be allowed to lodge any grounds of defence that they deemed relevant."

He added: "All in all, I find it rather a worrying session today in terms of delays and in terms of possible future restrictions on the defence."

All 259 people on board the Trans-Atlantic flight died when it exploded above the Scottish town on December 21 1988.

The wreckage which plunged to the ground also killed 11 Lockerbie residents.

end 201707 DEC 07