PIVOTAL Libyan figures in the Lockerbie tragedy have been sentenced to death, sparking concerns over the impact on future investigations into the massacre.

Former prime minister and foreign intelligence chief Abuzed Omar-Dorda is to be executed by firing squad, along with Saif al-Islam Gaddafi, the son of Muammar Gaddafi, for their roles during the country's 2011 civil war.

Omar-Dorda, who had also been Libya's permanent representative at the United Nations in New York, had been the key member of the Gaddafi regime facilitating the trail of the late Abdelbaset al-Megrahi at Camp Zeist in the Netherlands.

A Lockerbie inquiry was announced in late 2011 and Lord Advocate Frank Mulholland having travelled to the troubled North African country to help pave the way for it.

One expert on the 1988 atrocity, in which 270 people died, said the execution would remove one of the Libyans most prepared to work with the Scottish authorities.

The Tripoli court also sentenced to death seven others, including former Libyan spy chief Abdullah al-Senussi.

The Crown Office had previously commented on Senussi's potential value to the new inquiry when he was extradited from Mauritania, on the west coast of Africa, to Libya in September 2012.

Mr Mulholland and the FBI have previously stated their continuing belief Libya was behind the massacre and al-Megrahi carried out the operation.

But Professor Robert Black QC, one of the architects of the Camp Zeist trial which convicted al-Megrahi, has said that while the execution of Senussi would not have major implications for the Lockerbie case, Omar-Dorda's death may.

He said: "If Lockerbie was a Libyan operation, which I've yet to be convinced it was,I doubt if Senussi was in the loop. He was mainly concerned with internal security, ie keeping Gaddafi in power, rather than foreign operations.

"But the events in Tripoli do impact on Lockerbie in other ways. One of those sentenced to death is Abuzed Omar-Dorda, who was instrumental in brokering the arrangement that led the UK and USA eventually to agree to a non-jury trial in the Netherlands. A genuinely good guy."

Professor Black said another two Libyans with Lockerbie connections had been acquitted: Abdul Ati al-Obeidi, former Foreign Minister who chaired the Libyan government committee that dealt with securing a Lockerbie trial and, later, with the ramifications of the guilty verdict against Megrah, and Mohammed Zwai who was, for most of the relevant period during which the Lockerbie trial was being considered, Libyan ambassador in London.

Dr Jim Swire, the public face of the British families of the Lockerbie victims and sceptic over the role of al-Megrahi and Libya, said he believed the executions were "irrelevant" to resolve any outstanding questions over the tragedy.

But he also described the Tripoli decisions as a "put down for the concept of international justice".

He added: "I had hoped vainly these guys would be handed over to international criminal courts, given a fair trial and no death sentence imposed. They have been tried in a court which wouldn't be recognised outside Libya.

"I'm particularly sad about Dorda, who I knew well and met many times."

Libya has slid into chaos since the overthrow and killing of Gaddafi, who ruled the country for four decades.

The north African nation is split between rival militias and governments while facing an affiliate of the extremist Islamic State group.

The elected parliament and government is cornered in the country's east, with little power on the ground and an Islamist militia-backed government in the west that has seized Tripoli.

It is unlikely the sentence against Saif al-Islam Gaddafi will be carried out soon as a militia in western Libya has refused to hand him over to the government for the past four years.

The US-based Human Rights Watch said the trial was "undermined by serious due process violations" and called on the Libyan Supreme Court to independently review the verdict.

The Council of Europe said the case should have been turned over to the International Criminal Court at The Hague, which wants Saif al-Islam on charges of crimes against humanity.

During the trial, Saif al-Islam was accused of recruiting mercenaries who were given Libyan nationality, planning and carrying out attacks on civilian targets from the air, forming armed groups and shooting into crowds of demonstrators. Among the charges he was convicted of were incitement of murder and rape.

A Crown Office spokesman said: "We note the media reports of the sentence handed to Abdullah Senussi.

"Scottish Prosecutors continue to work with the Foreign and Commonwealth Office, United States and Libyan authorities despite the difficult situation in Libya to bring the others involved in the Lockerbie bombing to justice."