The man convicted of murdering Justin McAlroy, who was the son of a Labour Party donor and businessman, is seeking a fresh appeal with a dossier of new evidence.

William Gage, 36, was jailed for life and ordered to serve at least 20 years in 2004 for executing drug dealer Mr McAlroy, son of Tommy McAlroy.

Aamer Anwar, Gage's solicitor, has sent a 20-page document to the Scottish Criminal Cases Review Commission to ask it to refer the case back for a new appeal.

The SCCRC provided an interim report last year, which fell short of sending it back to court.

In 2006, the Court of Criminal Appeal in Edinburgh rejected Gage's appeal.

But Mr Anwar said there was "fresh evidence in relation to an alibi" and serious flaws in relation to the CCTV evidence and eyewitness identification.

Alex Neil, the SNP MSP, has also written to the SCCRC to ask it to re-investigate and look at the new evidence, which he believes makes the case worthy of a fresh appeal.

It was claimed that Gage shot Mr McAlroy, 28, five times outside his home in a row over a £50,000 drug debt. Gage has protested his innocence since he was jailed, claiming he was a victim of mistaken identity.

The prosecution pinned its case against Gage on a getaway car, a white Saab, which was later found burned-out. Police claimed Gage had driven the Saab from the murder scene in Cambuslang, Lanarkshire, to Easterhouse, Glasgow, a route lined with 43 CCTV cameras.

At the trial, it was stated that CCTV footage from the route was not available. However, after his conviction it was revealed that, in fact, there were some CCTV images, which showed no sign of the white Saab.

Mr Anwar said: "There are flaws and inconsistencies in every strand of the evidence they presented. We cannot close the door on this until it has been fully re-investigated. I think the SCCRC does a fantastic job, but I have concerns about the fact it is seriously under-resourced.

"There is new evidence in the case, including an alibi for Gage at the time of the murder."

Mr Neil said: "The CCTV evidence alone should be sufficient to justify a referral for appeal. Indeed, the trial judge himself cast doubt on the wisdom of the murderer abandoning' the Saab when and where he did.

"William Gage is in danger of losing at least 20 years of his freedom. It is incumbent upon the commission to deal with this case professionally and in sufficient depth to provide him with another chance to prove that he was not guilty of this crime.

"There is more than enough reasonable doubt in the evidence presented or not presented to the trial jury to justify a referral back to the appeal court in this case."

A spokesman for the SCCRC said: "The review into that case is still ongoing."

Justin McAlroy had been under surveillance by the Scottish Drugs Enforcement Agency for more than a year before his death in 2002.

The murder took place just days after he had attended a Labour fundraiser with then First Minister Jack McConnell and other senior party members, including then Health Secretary John Reid.

The event was one of the now infamous Red Rose Dinners, which raised funds for Mr McConnell and other Labour election campaigns from businessmen, including the building firm run by Tommy McAlroy.