Devolution has made it "almost impossible" for a Scot such as Gordon Brown to become Prime Minister, a senior Conservative said yesterday.

Alan Duncan spoke out as the Tories renewed their push to ban MPs from north of the border from voting on England-only issues at Westminster.

The bold bid to end to so-called "West Lothian" question will be recommended by a task force being led by former cabinet minister Kenneth Clarke, he revealed.

He said there was "no prospect of backing down on some form of English votes for English questions".

And the party indicated that it was "almost certain" to back such a proposal, which was included in the party's last manifesto.

Mr Duncan said it was "absolutely right" to stop MPs voting on issues that did not affect their constituents because they were now decided by the Scottish Parliament.

And he warned it could have serious constitutional implications.

"I'm beginning to think it is almost impossible now to have a Scottish Prime Minister because they would be at odds with the basic construction of the British constitution.

"It may be that the Labour Party has created this massive problem for themselves are are now regretting it," he said.

"We, the Conservatives, have a majority in England. We have MPs from Scotland essentially telling England what to do when they are doing the opposite in Scotland, have no control over what they are doing in their own constituencies in Scotland and are not in any way accountable for the effects their actions have in England."

Trade and Industry Secretary Alistair Darling spoke out against the Tory plan, saying it would introduce a two-tier system.

"I have always said that there is a huge problem of having two classes of MPs at Westminster," he said.

"I am a member of this Government, I am collectively responsible for everything they do and it would be very odd if you said, well I can't vote for it."

Liberal Democrat Sir Menzies Campbell, MP for North East Fife, warned against any "knee-jerk response" to the issue.

"A constitution is like a brick wall: if you take out one brick without regard to the strength of the wall, it all comes tumbling down," he added.

An opinion poll last week found most voters (55 per cent) believed Scots MPs should face a voting ban against 31 per cent who said the status quo should be retained.

But the same survey found more than half of those questioned (56 per cent) thought there was no reason why a Scottish MP should not become Prime Minister of the United Kingdom. A quarter, however, said Scots should be barred from the job.

The pressure to resolve the thorny question will be ramped up later this month if the Tories succeed in forcing a Commons debate on a Bill to enforce a ban.

The legislation was introduced in the Lords in February by Conservative former Home Secretary Lord Baker.

But it was dismissed as "lunacy" by Lord Chancellor Lord Falconer, who said it "betrays their [the Tories'] total lack of understanding of our constitution". ..SUPL: