A crowdfunder has been launched to help pay for the appeal against the conviction of the late Abdelbaset al-Megrahi for the Lockerbie bombing.

The attack on Pan Am flight 103, travelling from London to New York on December 21 1988, killed 270 people in the UK’s largest terrorist atrocity.

The lawyer representing Megrahi’s family claimed the Libyan government has “failed to honour its promise of funding the appeal” and is now asking the public for financial support.

Aamer Anwar said his legal team has worked on the appeal for free for more than six years and if charged the costs would run into millions.

The appeal hearing is due to start at the High Court in Edinburgh on Tuesday and is expected to last at least three days.

Former Libyan intelligence officer Megrahi – found guilty in 2001 of mass murder and jailed for life with a minimum term of 27 years – was the only person convicted of the bombing.

An appeal against his conviction was lodged after the Scottish Criminal Cases Review Commission (SCCRC) referred the case to the High Court in March, ruling a possible miscarriage of justice may have occurred.

Judges then granted his son Ali Al-Megrahi permission to proceed with the appeal in relation to the argument that “no reasonable jury” could have returned the verdict the court did, and on the grounds of non-disclosure of documents by the Crown.

Now, Mr Anwar said his legal team has been forced to ask the public for financial support for the case.

He said: “There has been a widespread assumption that our legal team have been paid fees to date, that is simply not true as they have worked pro-bono for what can only be described as the biggest criminal appeal in UK legal history.

“Despite promises over the course of several years, the Libyan Government has so far failed to fund the case and so we are now forced to look to the public to support us however much they can.

“In essence, our legal team has worked pro-bono for over six years.

“We accordingly have launched a crowdfunder to pay the costs accumulated over several years.”

He claimed it breaches Libyan constitutional law for one of its citizens not to be funded in a foreign court and said the team’s lawyer in Libya has filed a case against the government there.

Mr Anwar added: “In conclusion, for the Megrahi family and many of the British families of the victims supporting the appeal, there is finally hope this is the end of a very long journey.

“For my team it has been six long years but for the families we represent it has been nearly 32 years of struggle for truth and justice.”

Megrahi abandoned his initial appeal in 2009, shortly before his release from prison on compassionate grounds.

He died in 2012.

The UK Government and the Government of National Accord in Libya have been contacted for comment.