Labour have one high-profile dissident, former minister Malcolm Chisholm, but it is known that at least three LibDems have made clear that they back the release on compassionate grounds of Abdelbaset Ali Mohmed al Megrahi, who has terminal cancer.

It is understood that Liberal Democrat group rules contain a proviso that any conscience or moral matters must be afforded a free vote. This means that to maintain group unity they will have to come up with an amendment critical only of the handling of last week’s decision, rather than the decision itself.

LibDem leader Tavish Scott was critical of Megrahi’s release in Monday’s emergency session at Holyrood, as were Labour leader Iain Gray and Annabel Goldie of the Tories. But three LibDem MSPs have broken cover to say they thought Justice Secretary Kenny MacAskill made the right decision.

That dissent is a headache for Mr Scott and Mr Gray, who will be hoping that the three main opposition parties can unite around the strongest possible amendment.

The first indication of internal opposition to Mr Scott’s stance came on Monday when John Farquhar Munro, MSP for Ross, Skye and Inverness West, told BBC Radio Nan Gaidheal: “I’m of the opinion that Mr MacAskill had no other choice but the one he made.”

Then Central Scotland MSP Hugh O’Donnell said: “I thought the release of Megrahi in the circumstances was the right decision.”

Former Presiding Officer and one-time party leader Lord Steel has also clashed with Tavish Scott on the issue.

But LibDem MSPs say they have had emails critical of their party’s stance and veteran LibDem Glasgow councillor, Dr Christopher Mason, in a letter to The Herald, said: “I wish to state, as a Liberal Democrat, that I think Mr MacAskill’s decision to release Mr Megrahi on licence was right.”