Knife murderers should spend at least 16 years behind bars in an bid to tackle the “scourge” of Scotland’s blade culture, senior judges have said.

And child murderers, police killers and people convicted of firearms murders should not be freed for at least 20 years.

Terms of more than 30 years could also be handed out in cases that included mass murder by terrorists, the five judges said at the Court of Appeal in Edinburgh.

Murderers are handed mandatory life sentences but punishment parts have to be specified by judges.

The guidance was issued today after the judges decided on the minimum time three men sentenced for murder should serve before being considered for parole.

The Lord Advocate had appealed against the length of the men’s terms on the grounds that the disposal in each case was “unduly lenient”.

The Lord Advocate also invited the Court of Appeal in Edinburgh to issue guidance on sentences for murder.

The opinion of the court, released today, stated: “In our view there may well be cases (for example, mass murders by terrorist action) for which a punishment part of more than 30 years may, subject to any mitigatory considerations, be appropriate.

“A punishment part as low as 12 years would not be appropriate unless there were strong mitigatory circumstances, and a punishment part of less than 12 years should not be set in the absence of exceptional circumstances for example, where the offender is a child.”

The five judges, including Scotland’s most senior judge Lord Hamilton, also agreed that knife crime was “a scourge in the Scottish community”.

The judges said: “Other than in exceptional circumstances we would expect punishment parts in cases of that kind to be at least 16 years, and they might be significantly longer depending on the circumstances.”

The guidance also endorsed a view expressed in an earlier case that where the victim is a child, or a police officer acting in the execution of his duty, or where a firearm is used, a punishment part in the region of 20 years should be set.

The opinion added that the statements were “guidelines and should be treated as such”.

The three minimum terms being considered included Brian Boyle and Greig Maddock, who were convicted of the murder of Robert Bowie, who was kicked, stabbed in the leg, then set on fire on October 14, 2006, in Dunfermline. He died five days later in hospital.

Boyle assaulted and stabbed Mr Bowie in the leg and was then joined by Maddock. They placed Mr Bowie on a pyre of magazines, poured lighter fluid on him and set him alight while he was still alive.

Boyle had the punishment part of his sentence increased from 15 years to 20 years and Maddock saw his rise from 12 years to 18 years. Both men were convicted in June 2007.

The third appeal involved Robert Kelly who pled guilty to the murder of 64-year-old Agnes Mechen in Glasgow on August 30, 2002.

On July 25, 2007, Kelly was jailed after he admitted assaulting Mrs Mechen, placing a cord around her neck, tightening it and robbing her of a handbag, which contained between £180 and £200.

He concealed the body under a mound of soil or rubble.

Kelly’s minimum term was increased from 15 years to 19 years.

In terms of reducing the length of sentences for guilty pleas to murder at the earliest opportunity, the opinion said: “We agree that in murder cases the maximum discount should be about one sixth.”