Six members of Abdelbaset Ali Mohmed al Megrahi's immediate family have joined forces with a number of British relatives of those who died in the terrorist atrocity to seek a third appeal against his conviction in the Scottish courts.
Their lawyers claim to have uncovered evidence that members of the Scottish Government put pressure on him to drop his previous appeal in exchange for being freed.
They also say forensic evidence at Megrahi's trial at Camp Zeist in the Netherlands in 2000 was flawed and allege that witnesses were in the pay of the US Secret Service, leading to a miscarriage of justice.
Megrahi, who died from cancer in May 2012, was the only person found guilty of the bombing of Pan Am flight 103 over the Dumfries and Galloway town on December 21, 1988, in which 270 people were killed.
He abandoned a second appeal against conviction in 2009 when he was dying from prostate cancer. He was later released from jail by the Scottish Government on compassionate grounds.
The group yesterday lodged an application with the Scottish Criminal Cases Review Commission (SCCRC), which refers suspected miscarriage of justice back to the High Court.
Aamer Anwar, the Glasgow-based lawyer who is taking the case to the SCCRC, said: "To date both the British and Scottish governments have claimed that they played no role in pressuring Megrahi into dropping his appeal as a condition of his immediate release.
"However, the evidence submitted to the Commission today claims that this is fundamentally untrue."
Mr Anwar said it is the first time in legal history that relatives of murdered victims have united with the relatives of a convicted dead person to seek justice using a referral to the appeal court.
Quoting Megrahi's relatives, he said: "'We, the family of Abdelbaset al Megrahi, will keep fighting for justice to find out who was responsible for 271 victims of the Lockerbie disaster'.
"They of course include Mr Megrahi as its 271st victim."
Campaigner Dr Jim Swire, whose daughter Flora died in the bombing, has long held the view Megrahi was not guilty of the atrocity and gave his backing to the bid to overturn the conviction.
He said: "If you had a daughter who was 23 and who was both beautiful and highly intelligent and she was brutally murdered in a situation where it's clear that the national protection and security services had abysmally failed, do you not think that even 25 years later you might want to feel that you had a say in discovering who murdered her and why she was not protected?
"I think you would find you have that need, as I do and as many relatives do. That's our only reason for being here."
He believes the fact that Megrahi's own family have now chosen to take forward a fresh appeal bid could boost its chances of getting back to court.
Dr Swire has previously said they could be risking their lives if they raise the prospect of launching a fresh appeal against the conviction.
The SCCRC confirmed it had received an application to review Megrahi's conviction.
A Scottish Government spokesman said: "Mr al Megrahi was convicted in a court of law, his conviction was upheld on appeal and that is the only appropriate place for his guilt or innocence to be determined.
"The Scottish Government has always been clear that it is for relatives of Mr al Megrahi or relatives of the Lockerbie bombing victims to decide whether to apply to the SCCRC to ask them to consider referring Mr al Megrahi's case back to court."