Lockerbie bomber Abdelbaset al-Megrahi will be released from Greenock Prison on compassionate grounds, STV News sources have learned.

The decision to release him was made by Justice Secretary Kenny MacAskill.

He will be freed by Thursday afternoon.

Megrahi was being held in Greenock Prison serving a life sentence with a minimum of 27 years after being convicted in 2001 of the 1988 bombing of Pan Am Flight 103 which killed 270 people.

Megrahi has terminal prostate cancer, and his condition has deteriorated.

On Tuesday judges at the High Court in Edinburgh accepted a bid from Megrahi's legal team to formally abandon their second appeal against his conviction and sentence. They heard that Megrahi's condition was worsening and that he was anxious to spend what little time he has left with his family. His legal team said that Megrahi had a "Very aggressive cancer", his condition was "grave" and "the prognosis is extremely limited."

Justice Secretary Kenny MacAskill has been under pressure as speculation grew that Megrahi was likely to be released.

The decision on whether or not Megrahi should remain in prison had divided the families of survivors, with some insisting that he should remain in jail for the rest of his life, others maintaining that release was appropriate given his circumstances.

There were calls from MSPs from across the political spectrum to recall parliament to debate the issue.

Earlier this week, US Secretary of State Hillary Clinton said it was "absolutely wrong" to release him. She had spoken to Mr MacAskill last week to say Megrahi should remain in jail in Scotland. A survey at the weekend suggested that the majority of Scots believed that Megrahi should remain behind bars.

The Justice Secretary had received a recommendation from the governor of Greenock prison that Megrahi be released on the grounds of his health.  Rules allow for release if a condition is likely to result in the death of the prisoner in the near future - three months is used as a guideline.

First Minister Alex Salmond said on Tuesday that he would "absolutely trust" his Justice Secretary to reach the right decision over Megrahi.