THE UK Government attempting to change who can vote in indyref2 risks invalidating the result – and would have to be agreed to by the Scottish Government, according to experts.

Reports last week suggested Cabinet ministers are urging Boris Johnson to step up the fight to save the Union by allowing Scots anywhere in the UK to vote on independence.

Constitutional experts say there would be practical problems identifying who is eligible and warn one side changing the rules unilaterally would lead to the results being challenged.

Another key issue is that electoral law has been devolved to Scotland, meaning it has powers over determining the “model” of a referendum, a legal academic has pointed out.

Around 800,000 people who were born in Scotland now live in England and up to 50,000 live in Wales. Most are thought to be pro-Union and their inclusion could swing the vote against independence, according to polling experts.

One Cabinet minister was reported as saying: “We know Sturgeon will start trying to force another referendum as soon as she thinks it is politically tenable again, so there are things we can and should do now to be ready for her.

“One thing is to open up eligibility of the vote to all Scots in the UK, not just those living in Scotland.”

However James Mitchell, professor of public policy at the University of Edinburgh, said he doubted the suggestion to extend the electorate in this way was serious.

“There would be practical problems identifying who would be eligible,” he said. Would this extended electorate have to apply to vote? Presumably there would need to be a campaign to inform potential electors elsewhere in the UK.

“If it included Northern Ireland, we can be sure that many would vote according to preferences related to Northern Ireland’s constitutional status and with scant regard for the Scottish question.”

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Mitchell (below) said any future referendum would require agreement in advance of any campaign on the rules, conduct and how the results should be interpreted.

“There would be little point holding a referendum if the result was disputed or challenged fundamentally,” he added.

“The problem is that any unilateral change to rules by either government would likely lead to boycott, undermining turnout and thereby delegitimising the result.”

Dr Alan Renwick, deputy director of the constitution unit at University College London, last week published a blog on five ways in which referendums could be improved after Brexit.

He said that “pretty much everyone” would now agree the vote on leaving the EU was an example of how not to run a referendum.

“A theme across all of our points in that blog is to give people the greatest possible clarity on the choice that faces them,” he said.

“If you are voting on something like independence where some things would only be decided after a vote in favour of independence through negotiations, then obviously you can’t set those out. But at least set out what the process is – in the 2016 referendum no-one ever mentioned Article 50, the actual process that Brexit would happen through.”

Renwick said the UK Government had “essentially accepted” the principle that Scotland has the right of self-determination in the Edinburgh Agreement, which set out the terms for the 2014 referendum.

“Given that it has accepted that, then it ought to accept the principle that it has a duty in the context of any referendum to enable the people of Scotland to exercise that right fairly,” he added.

“If you try to tailor the franchise to a particular vote you just end up politicising the franchise and it becomes not a matter of principle, but a matter of political power. That delegitimises the vote.

“So if the Union won very narrowly and it was clear it had won only because the franchise had been changed from the normal franchise, then that doesn’t produce a result which is going to command universal respect by any means.”

The National:

Dr Nick McKerrell, a senior lecturer in law at Glasgow Caledonian University, said the suggestion to extend the vote to all Scots in the UK looked like a “negotiating position”.

He pointed out the Scotland Act of 2016 devolved electoral law to Scotland, unlike in 2014 when those powers were with the UK Government.

“If there is a referendum then the law about it will be determined by the Scottish Parliament,” he said.

“This is tied up with whether they get ‘permission’ to do the referendum, because the Scottish Government would have to agree to any changes to the election.

“It is not one-sided, the UK Government couldn’t say we are setting the law for the referendum and it is everybody who is Scottish can vote in it.

“That can’t happen – the Scottish Government would have to agree to that, which I don’t see them doing. It’s sort of playing games a bit.”

The Scottish devolution referendum of 1979 recorded a narrow majority for Yes but a stipulation that 40% of the whole electorate had to vote in favour meant plans did not progress.

McKerrell said while the UK Government could try to negotiate for a requirement such as a minimum 50% turnout, it would have to be agreed to. “[The Scottish Government] want a Section 30 Order, so they need to do a degree of negotiation, but the model of election will be determined by Scotland itself,” he added.