The YouGov poll of 1556 people found 45% thought Mr MacAskill made the right call to free Abdelbaset Ali Mohmed al Megrahi last month on compassionate grounds. The same percentage said he was wrong.

It shows a swing in support for the release following a BBC poll last Friday, when only 32% supported it. The poll came on the day the SNP government launched its third legislative programme including a Referendum Bill. It includes 13 bills headed by the flagship proposal that is almost certain to be voted down by the opposition parties.

First Minister Alex Salmond urged the other parties to “let the people speak” as he set out his government’s plans for a referendum on independence but Labour leader Iain Gray branded it a “flagship waiting to be scuttled”.

Meanwhile, the Megrahi row continued when Sir Christopher Meyer, the UK ambassador to Washington at the time of the negotiations to bring the Libyan to trial, yesterday claimed the US was given the “clear political and diplomatic understanding” that he would serve his full sentence in Scotland.

Downing Street also said the Prime Minster had not endorsed Mr MacAskill’s decision, after it was earlier confirmed that Gordon Brown did not want the Libyan to die in a Scottish prison.

The research, for the SNP on Tuesday and Wednesday, found 49% of white-collar workers were in favour with 43% against. Support among blue-collar workers was 41% while 47% disagreed.

There was a difference in opinion among age groups. Between the ages of 18 to 34, support levelled out at 39% but among the over-55s, it reached 55%.

Almost half of those questioned (49%) said Nelson Mandela’s support for Megrahi’s release had enhanced Scotland’s reputation, but a quarter said it had been damaged.

A spokesman for Mr MacAskill said: “The poll demonstrates a very substantial shift of opinion towards support for the Justice Secretary’s decision.”