DAVID Cameron has brushed aside Nicola Sturgeon's argument that there should be no British exit from the European Union without all four nations of the UK voting in favour of it, insisting "we are one United Kingdom".

But the First-Minister-in-waiting's proposal that the EU Referendum Bill be amended "to give proper protection to any of the four nations of the UK being removed from the EU against their will" has won the support of academics.

Professor Sionaidh Douglas-Scott of Oxford University argued it was "with the devolution settlement itself that an EU exit would wreak the most havoc, risking a constitutional crisis" without measures similar to those being proposed by Ms Sturgeon.

Paul Cairney, professor of Politics at Stirling University, noted that a referendum in which Britain as a whole voted to leave the EU but Scots voted to stay would trigger a UK constitutional crisis and demands for a new independence referendum.

"I don't think anyone would want something so important to be triggered in such a crisis-like way, so Ms Sturgeon's proposal seems like a pragmatic way to ward off that possibility."

Last week, a study by Durham and East Anglia universities showed England would vote to leave the EU while Scotland would vote to stay in. Ahead of a rally last night, the Deputy First Minister said she was proposing a double majority of the kind found in many federal states when major constitutional change was proposed; that withdrawal of the UK from the EU would not only require a majority across the UK but also in each of its four constituent parts.

"What that reflects is the UK - and we were told this regularly during the Scottish independence referendum - is a family of nations; it's not a unitary state," said Ms Sturgeon "When something is being proposed that will have significant implications for the economy, for jobs, for the standing in the world of each of those four nations, then surely our voice should have equal status."

However, No 10 made clear the PM "did not accept the premise" of Ms Sturgeon's argument, noting: "The people of Scotland have expressed their view through the referendum and the Prime Minister is determined that all citizens of the UK have the right to express their view in the referendum by the end of 2017."

Later in the Commons, Mr Cameron added: "We are one United Kingdom. There will be one in/out referendum and that will be decided on a majority of those who vote; that is how the rules should work."

In a recent article, Ms Douglas-Scott pointed out that EU law and the European Convention on Human Rights were incorporated directly into the statutes in Scotland, Wales and Northern Ireland. She argued that a Legislative Consent Motion being enforced without consent would run contrary to the pre-referendum "vow" enshrining the rights of Holyrood and run counter to the Scottish legal principle of popular sovereignty .

She also raised the possibility of each of the devolved nations holding their own referendums and a federal standard set whereby UK withdrawal was only possible if a majority of the devolved nations voted to leave the EU.

Anas Sarwar, Scottish Labour's interim leader, asked if the need for a four-nation agreement on constitutional change would also be Ms Sturgeon's "position on any future independence referendum, or is she again trying to face different ways at the same time?"

Jackson Carlaw for the Scottish Conservatives insisted Scots had voted to remain within the unitary state of the UK, and added: "Going by Nicola Sturgeon's logic, the rest of the UK should have been given a vote in the independence referendum."