INDEPENDENCE for Scotland would splinter the UK and leave Wales as a separate nation, a key ally of Prime Minister Tony Blair will warn this weekend.
The comments by Lord Falconer, the Lord Chancellor, reflect a growing nervousness in Labour ranks that the SNP is polling strongly ahead of May's elections in Scotland and Wales.
His warning is the first attempt by a senior minister to link an SNP win with consequences beyond Hadrian's Wall.
The SNP has said it would hold a referendum on Scottish independence if it wins power in May, and Lord Falconer - a former flatmate of Mr Blair's - will say Wales' relationship with England would be "in doubt" if Scotland voted "yes".
In an interview with GMTV to be broadcast tomorrow, he said, "If Scotland went then I think the relationship with Wales and Northern Ireland would then be in doubt it seems to me, and the abolition of the United Kingdom, which is what it would amount to, in my view would be very detrimental to the prosperity of the people of the United Kingdom and as well the standing of the individual nations in the world.
"How much better can the United Kingdom argue for the interests of the individual Scot or the individual English in, for example the European Union, than England could or Scotland could?"
He said the UK would become "weakened in the world" if it simply became Wales, England and Scotland.
"It would be to the detriment to the people of England if the Union broke down - so much stronger as part of the United Kingdom than simply part of England, Wales and Northern Ireland," he said.
"And how long would the link between Wales and Northern Ireland last if Scotland went?"
Scotland has had a parliament with full law-making powers since 1999, and the SNP believes it can capitalise on the unpopularity of the Labour government to become the largest party in May; a poll in November put the SNP on 34% and Labour on 29%.
While the SNP is pushing for a referendum on independence, Plaid Cymru revealed this week that its strategy would be a poll on whether Wales should have a full parliament - what Scotland has today - to be held in 2011.
In his interview, Lord Falconer admitted that the relationship between various parts of the UK has been put "much more under the spotlight" as a result of devolution. But he denied the perceived threat to the future of the UK was a problem of the Government's own making.
He said, "Suppose that we had said no to devolution in 1997, that was after a period of time where the Scottish people, as they subsequently expressed in a referendum, were extremely keen on having devolution, suppose that we had said no, I'm absolutely sure that the demands for independence would be much much stronger than they are now.
"I completely reject the argument that devolution has caused the current position, look at the facts: we've been in power as a Government in Westminster for three terms, this is the third election for the Scottish Parliament, it is inevitable that there would be, as it were, a by-election factor."
Plaid leader Ieuan Wyn Jones said last night, "Lord Falconer's comments are a further sign of Labour hitting the panic button.
"What we need is proper and mature debate on the relationship between Wales, Scotland, Northern Ireland and England. Essentially, and most importantly, it should be up to the people to decide on their constitutional future.
"Successive London Governments have put the interests of the south east of England before those of Wales, Scotland and Northern Ireland; what Plaid wants is strong and fair representation for all the people of Wales to bring real benefits to our country."
Mike German, leader of the Liberal Democrats in the Assembly, said, "It's funny that the party which had no problem introducing an unbalanced and unfair asymmetric devolution, is now crying foul when the Celtic nations look set to reject Labour."
Labour was "panicking" and had become obsessed with other parties' policies, said Mr German, whose favoured solution is a federal UK.
Elsewhere in his interview Lord Falconer said Chancellor Gordon Brown was a "towering figure" in the Labour Party.
A Brown leadership when Mr Blair steps down this year was "the most likely course" for the party, he said, although he did not rule out other possibilities.
The Lord Chancellor also ruled out any review of the Barnett formula, which allocates money from the Treasury to the Assembly based on population.