The teenager who abducted, raped and murdered six-year-old Alesha MacPhail has had his minimum prison sentence cut by three years after winning his appeal.

Aaron Campbell, who was 16 when he killed the schoolgirl on the Isle of Bute in July 2018, denied the charges throughout a two-week trial earlier this year, but then admitted the offence during his sentencing hearing in March.

Judge Lord Matthews handed Campbell, now 17, a mandatory life sentence and ordered him to spend at least 27 years behind bars.

The minimum term he will serve before being considered for parole has now been reduced from 27 years to 24 due to his age at the time of the murder.

The decision was made by Lord Drummond Young, Lord Menzies and Lord Justice Clerk after an appeal hearing at the High Court in Edinburgh on August 7.

During the hearing, Campbell's lawyer, Brian McConnachie, had argued the killer's jail term is "extraordinarily" long and a "miscarriage of justice".

He added that by serving his full sentence, Campbell won't be able to properly mature in jail.

The ruling by the three judges on Tuesday said: "Against the cases to which we have made reference, a punishment part in excess of 20 years was plainly merited.

"We have concluded that a punishment part of 24 years would be appropriate to reflect the appellant's youth.

"We will accordingly allow the appeal to the extent of substituting that period for the sentence imposed."

They added: "As with all punishment parts, this is not an indication of the date when the appellant will be released.

"It specifies rather the period which must pass before the appellant may even apply for parole.

"As the trial judge had observed ... 'whether (the appellant) will ever be released will be for others to determine but as matters stand a lot of work will have to be done to change (the appellant) before that could be considered - it may even be impossible'."

Scottish Conservative shadow justice secretary Liam Kerr said: "This is one of the most vile criminals in Scotland, and he should not be enjoying having time shaved off his sentence.

"If anything, he should be looking at an even longer stint.

"Yet again, Scotland's justice system has come down favourably on the side of the criminal, and it will cause massive upset to the victim's family.

"In short, this is a quite disgraceful outcome."

Following the judges' decision, Alesha's uncle, CJ MacPhail, said: "As most of you are about to find out today we have found out the monster that abducted, murdered and raped has had his appeal granted by the court in Edinburgh.

"What this means is instead of already been given a lesser sentence as child at 27 year the judges have now said this has been reduced to 24 before he can be considered for release.

"They told us it [would] be very unlikely for him to be granted an appeal, they told us it would be unlikely for him to be granted the reduction on his sentence.

"So how can we believe when they say he is unlikely to be released?"

Alesha, from Airdrie, North Lanarkshire, was only a few days into a family holiday on the Isle of Bute when she was targeted by Campbell.

Armed with a knife, he snatched her from her bed before carrying her to the former Kyles Hydropathic Hotel on the island where he raped and murdered her on July 2 last year.

Campbell told the child he was a friend of her dad's and was going to take her home, before raping and murdering her.

He then threw his clothing into the sea before going back to the scene to retrieve his phone.

During the sentencing, Lord Matthews told how he was "shocked" when he read the "cold-blooded and horrific" account given by the killer to a psychologist after his conviction.

Alesha's body was found in a wooded area of the island a few hours after her family reported her missing.

Campbell previously claimed Alesha's dad's girlfriend, Toni McLachlan, had "murder on her mind", blaming her for the killing.

However, it was reaffirmed during the sentencing hearing that Ms McLachlan had nothing to do with it.