Lord Wallace Of Tankerness, Scotland's Advocate General, will confirm today that the Scottish Parliament could not trigger an independence referendum. The government's top legal adviser on Scottish law will contradict claims by Alex Salmond, who believes that he could iniate an advisory referendum without consultation with London.
Lord Wallace will give a lecture in Glasgow, where he will say there is no meaningful difference in law between a non-advisory and legally-binding one.
"A referendum must do something, and mean something, otherwise it is hardly a proper use of public money," he will say. "It would not have a purpose in its own right and it is not merely an opinion poll – a referendum is, or at least purports to be, a form of political decision making, where a decision is best made directly by the public rather than by their representatives in Parliament.
"If, as the law currently stands, the Scottish Government were to proceed with this legislation, it would be open to challenge in the courts. It is the view of the UK Government that such a challenge is likely to be successful."
Lord Wallace, a former Deputy First Minister of Scotland and Scottish Liberal Democrat party leader, says: "If, as the law currently stands, the Scottish Government were to proceed with this legislation, it would be open to challenge in the courts.
"It is the view of the UK Government that such a challenge is likely to be successful.
"It could be initiated in the Court of Session by any individual or organisation which could demonstrate sufficient interest to bring proceedings.
"The challenge could invalidate the outcome of the referendum, it would cause delay, and it could stop any referendum from happening in the first place."
A spokesman for Scotland's First Minister, Alex Salmond, said: "The UK Government has published its opinion, not its legal advice - and the Scottish Government have set out our position in a number of documents since May 2007.
"We are entirely confident about our legal basis to hold a consultative referendum - as confirmed by a range of experts.
"In any event, we have absolutely no objection to a Section 30 enhancement of Holyrood's powers to hold a legally binding referendum, but what we cannot possibly accept is Westminster dictating the terms of Scotland's referendum.
"The Westminster parties should have a care, for their own sake - they have badly misjudged this issue, and badly misjudged the mood of people in Scotland.
"The sabre rattling of the Westminster parties - ganging up with each other, and trying to bounce Scotland into an early referendum and dictate the terms - has seen support for independence already reach 40%."
Talks are due to take place between the governments in London and Edinburgh later this month, where the government is expected to attempt to pin Alex Salmond down on conentious issues, particularly whether the referendum's ballot paper had just one question - a simple in-or-out choice