THREE High Court judges will be asked to lay down the law of Scotland in the case of the three Trident protesters acquitted last week at Greenock Sheriff Court.

The Lord Advocate said yesterday he intended to refer the case to the Court of Criminal Appeal for a ruling.

The Crown has no right of appeal against an acquittal in a jury trial but can ask for an authoritative legal ruling which settles the law although it does not affect the outcome of the case. The procedure, known as a Lord Advocate's reference, is provided for in the Criminal Justice (Scotland) Act 1980 but has been used in only a handful of cases since then.

A Crown Office spokesman said yesterday: ''In reaching his decision the Lord Advocate (Lord Hardie) considered a report from the procurator-fiscal at Dunoon after Sheriff Margaret Gimblett directed a jury to acquit Angela Zelter, Bodil Rodder and Ellen Moxley.''

All were charged with causing #80,000 worth of damage to a Trident nuclear research barge.

After a four-week trial Sheriff Gimblett directed the jury to acquit the women on charges of maliciously damaging the barge and lab equipment at Faslane naval base near Lochgoilhead.

Sheriff Gimblett was quoted as saying: ''The three took the view that Trident was illegal and, given the horrendous nature of nuclear weapons, that they had an obligation in terms of international law to do whatever they could to stop the deployment and use of nuclear weapons in situations construed as a threat. I have heard nothing which would make it seem to me that the accused acted with criminal intent.''

The sheriff was reported to have accepted the argument that nuclear weapons were illegal under international law and that the women were acting to prevent a crime.

She was referred to an opinion by the International Court of Justice in 1996 about the possession of nuclear weapons which was also cited to three High Court judges in a Scottish appeal in July.

In the case in July Lord Coulsfield, sitting with Lords Milligan and Cowie, ruled that peace protester Helen John's sincere belief about the illegality of nuclear weapons and their potentially appalling consequences did not provide a reasonable excuse for cutting part of the perimeter fence at Coulport naval base in Loch Long.

Ms John cited the 1996 decision of the International Court of Justice, but Lord Coulsfield said: ''The advisory opinion of the International Court of Justice does not hold that it is contrary to international law for a state to possess nuclear weapons.

''The majority view was that the threat or use of nuclear weapons would be, in general, illegal but that it might, in the last resort, not be illegal to use such weapons in self-defence against a threat of national extinction.''

An appeal court decision must be followed by Sheriff Gimblett but in a letter published in Tuesday's Herald, Mr Matthew Berlow, a solicitor who was part of the Trident defence team at Greenock, said the International Court decision had expressly not been relied on in arguments before the sheriff.

According to Mr Berlow the sheriff accepted the argument that Trident was being used as a threat to other nations and that the accused had wilfully but not maliciously exercised their legal right to prevent a crime.

The Trident Ploughshares campaign last night welcomed the referral to the Court of Criminal Appeal. A spokesperson said: ''We have been looking forward to the day when the legality of Trident would be properly debated at this level. We are ready to demonstrate again that Britain's nuclear weapons system is utterly irreconcilable with the principles of international humanitarian law.''