Prosecution authorities and the Government were blocking progress towards a trial and had 'abandoned' the victims and their families, they said.
Under the new plan, put forward by Robert Black, an Edinburgh University law professor, a Scottish prosecutor would present the case against the two men before a panel of judges in the International Court of Justice in the Hague.
Earlier this month Omar al- Muntasser, the Libyan foreign minister, approved the plan and Colonel Muammar Gaddafi repeated Libya's acceptance in a speech on Saturday.
Lawyers representing the suspects described it as constructive. But a spokesman for Lord Rodger of Earlsferry, Scotland's senior law officer, dismissed the proposals as unworkable. 'There is no legal machinery to try the two accused in an international tribunal,' he said. The Foreign Office said the suspects could only be tried in a British or American court.
Abdelbaset Ali Mohmed Al Megrahi and Al Amin Khalifa Fhima have refused to surrender for trial in Britain or America, arguing that a jury would be prejudiced against them.
International lawyers say a special court could be set up to try the men. Rob Siekmann, for the Asser Institute of International Law, said: 'If states and international organisations agree, they can do anything. If the countries involved requested the UN Secretary General to create an ad hoc tribunal for the trial, he could ask the Security Council to do so but it would have to be something new - like the Yugoslavia war crimes tribunal.'
A UN tribunal was set up in the Hague last year to try those accused of committing crimes against humanity in the war in the Balkans.
Dr Jim Swire, spokesman for British relatives of the 270 people killed in December 1988, said last night: 'Britain, as a member of the United Nations Security Council, voted to set up the Yugoslavia war crimes tribunal. Five years after the biggest mass murder in British criminal history, they will not agree to similar plans to try the accused.
'We have made it clear that we want a trial because we cannot begin to come to terms with the tragedy until we know why it happened and who ordered it. If there was an ounce of political will, the new proposals would have been implemented. The Government has abandoned the victims and their relatives.'
Professor Black last night described the Government's rejection as disappointing. 'It is the British government which is blocking progress. They do not appear to want a trial,' he said.Reuse content