There will be no posthumous royal pardon after more than two centuries for a man hanged for abetting a murderer who was never arrested or charged, never mind convicted.

Those who have campaigned to clear the name of James Stewart say the fact the crime was committed 263 years ago doesn’t diminish the injustice of hanging an innocent man.

They have now been told that a pardon will not be forthcoming despite the overwhelming evidence that says Stewart was wronged.

On the afternoon of May 14, 1752, a prominent Hanoverian figure was riding in the woods near where the Ballachulish Bridge now stands, when he was shot dead.

Colin Campbell of Glenure had been on his way to evict some of the Jacobite Stewart clan from their land.

The murder was integral to the plot of Robert Louis Stevenson's celebrated novel Kidnapped, set after the Jacobite cause had been crushed at Culloden.

The original indictment named Ailean Breac Stewart (Allan Breck in Kidnapped) as the guilty party for murder, and James Stewart as guilty of abetting him.

Stewart is popularly held to have been tried in a kangaroo court in Inveraray in September 1752. Eleven of the 15-strong jury were Campbells, and the senior judge their clan chief.

The court sat without break from five on Friday morning until seven on the Sunday morning, leaving one juror to shout at a defence advocate: "Pray sir, cut it short. We have had enough."

Five and a half years ago Glasgow solicitor John Macaulay petitioned ministers to overturn what is seen by many as one of the most blatant miscarriages of justice in Scottish legal history.

The Scottish Government could recommend to the queen that the Royal Prerogative of Mercy (RPM) be exercised and that Stewart receives a free pardon for his alleged role in what became known as the Appin Murder.

But a Scottish Government civil servant has finally replied to Mr Macaulay declining his application, explaining that the First Minister’s powers to intervene are “necessarily used sparingly".

It quotes judge and legal scholar Baron David Hume (nephew of the famous Scottish philosopher), who wrote 45 years after the trial “I see no reason to believe that the verdict was not according to the justice of the case, or different from what the jury were warranted to return upon the evidence laid before them.”

It also quotes from the book by the late American historian Lee Holcombe on the reasons the Campbells had to suspect James Stewart and says: ”We have concluded that the grant of a Royal Pardon would not be justified on the application of the ‘clean hands’ doctrine that new evidence had come to light which demonstrated conclusively that no offence was committed or that the individual concerned did not commit the offence.”

Mr Macaulay said: “The most important aspect, the basis on which the submission was made, has been ignored completely and deliberately. Our submission was that, quite irrespective of all other ‘evidence’ led at trial, as Allan Breck could not be identified as the assailant, nor inferred as such, the case against James Stewart fell completely as a matter of law.”

But it was more than a story to Mr Macaulay's client John Campbell from Motherwell.

A former lorry driver, he spent almost 20 years researching the history before instructing his solicitor to take up the case. Now 69 he simply can’t understand how the conviction can still stand.

In 2008 Mr Macaulay unsuccessfully applied to the Criminal Cases Review Commission.

In his book on the murder, Culloden and the Last Clansman, Highland historian Professor Jim Hunter argues that while James was not guilty, a murder conspiracy had indeed been hatched by the Stewarts of Appin, including Ailean Breac.

A group of experts invited to re-examine the case by the Royal Society of Edinburgh two years ago, found the evidence pointed to two unknown gunmen; and concluded that James Stewart was not guilty, and the main suspect Ailean Breac was not responsible either.