The Appeal Court in Edinburgh has decided to appoint a special defender to view confidential documents thought to contain vital information about the electronic timer that detonated the Lockerbie bomb.

The Appeal Court in Edinburgh has decided to appoint a special defender to view confidential documents thought to contain vital information about the electronic timer that detonated the Lockerbie bomb.

The decision follows an unprecedented hearing, held behind closed doors, at which the UK Government argued that revealing the documents would compromise security.

The Advocate general, who represents the UK Government in Scottish courts, asked the court to appoint a security-vetted lawyer who could look at the documents on behalf of the defence team of Abdelbaset Ali Mohmed al Megrahi, the Libyan convicted of the bombing.

This special defender would then argue which parts of the document should be published - although judges would make the final decision about how much, if anything, should be revealed.

So far the court has not published its decision, but Foreign Office minister Kim Howells has written a letter confirming that the court has decided to appoint a special defender.

It will be the first time such a course has been taken in Scotland, although some English courts have appointed special defenders to examine evidence in terrorism cases.

There has been no official comment from Megrahi's legal team, although it is thought it is planning an appeal to the Privy Council, arguing that the move will violate his human rights.

The team's decision on whether to appeal is expected to hinge on the extent to which special defenders will be used in the hearing. One of the documents, which originated in an unknown foreign country, is thought to contain vital information about the timer to the bomb that killed 270 people over Lockerbie in 1988.

David Miliband, the Foreign Secretary, has already said the document should remain confidential.

However, Megrahi's defence team believes the failure to disclose the document calls into question the ultimate right to a fair hearing.

The document from an undisclosed foreign country was uncovered during the three-year investigation of the Scottish Criminal Cases Review Commission, which resulted in the case being referred back to the courts for a new appeal last summer.

The commission concluded that the failure to disclose the document during the original trial could constitute a miscarriage of justice.

Although the Crown allowed the commission to see the material, it has refused to disclose it to Megrahi's defence team.

Mr Miliband says that to hand over the documents to defence lawyers would put national security at risk.

Lord Hamilton, the Lord President and Scotland's top judge, sat with Lords Kingarth and Eassie last month to decide whether Megrahi can still get a fair hearing without access to the papers.

Lord Davidson of Clova, QC, the Advocate General, who represents the UK Government on legal matters in Scotland, has previously asked to put the Foreign Secretary's case behind closed doors.

The public interest immunity argument has been lodged by Lord Davidson - not the Crown Office in Scotland.

It is the first time that Scottish courts have needed to deal with such a question in closed court.