IN December this year it will be 20 years since 270 people - passengers, crew and residents of Lockerbie - died when Pan Am flight 103 was blown out of the sky. After one of the most complex and detailed terrorist investigations ever mounted into a mass murder, a Libyan was convicted and is currently serving life in a Scottish jail. Abdelbaset Ali Mohmed al-Megrahi has already had his case brought before a court of appeal and had it dismissed. It was re-examined to ensure there had been no miscarriage of justice, that the verdict was beyond reasonable doubt and that, crucially, he had received what should be the mark of any civilised country: a robust and fair trial.

For exactly the same legal reasons, the Scottish Criminal Cases Review Commission last year granted leave for a second appeal. It knew its decision would be extending the longest, most expensive and most high-profile case ever brought before a Scottish court. The aim of this second appeal is once again straightforward: to ask whether the initial verdict was sound. Once again, for proceedings to be seen as fair and just, al-Megrahi has a right to be told the full nature of the Crown's evidence against him. And for that to happen under any statutory definition of justice, there must be disclosure of this evidence in order for his defence team to present their case the best they can.

The decision to re-examine the conviction was justified when it became clear that documentary evidence given to the Scottish police in 1996, said to be from an unnamed foreign government, was kept from al-Megrahi's counsel.

The Lord Advocate, Elish Angiolini, QC, has now indicated that she wants to release this material. As an experienced Queen's Counsel she will know her decision is not abstract or difficult to comprehend, but based on the simple principles of justice and the entitlement to a fair trial. The overriding requirement of her office is to ensure there are mechanisms in place which will ensure the delivery of a fair trail.

Foreign Secretary David Miliband, and by implication Gordon Brown's government, doesn't see things this way. The Foreign Office has said it is not in the public interest to release the documents, and that they were initially given to UK authorities on the understanding they would not be made public.

Miliband's decision to sign a public interest immunity certificate that prevents disclosure to al-Megrahi's defence of this potentially crucial evidence, ignoring and over-ruling the wishes of the Lord Advocate, is a disgraceful one that will do nothing for the international reputation of British justice. Since when was it in the public interest to treat a court of law as though it were an inconvenience in a wider game of supposed diplomatic back-door dealings?

There is of course a wider constitutional implication at stake, with a Westminster Cabinet member threatening the statutory independence of Scottish courts. For al-Megrahi, and for the families of those who lost their lives in and above Lockerbie and who want justice to be done, Miliband is making a mockery of the appeal proceedings.

More poignant questions for the Foreign Office centre on why it sees it necessary to overrule the Lord Advocate; why it would risk an unsound verdict in order to protect an agreement with an unnamed foreign country; and, perhaps the most disturbing of all, why it no longer has any faith in Scottish courts, or any court of law.

This second appeal should be the arena where all we know of the Lockerbie bombing is laid bare - something which, after 20 years, we should already know. The games the Foreign Office is playing will prevent this happening.