THE former head of Downing Street’s Union Unit believes the Tories should change the law to prevent Holyrood from holding a second independence referendum until at least 2034.

Luke Graham, who was sacked from his role on the Union Unit in February following Boris Johnson's highly criticised trip to Scotland in February, argued a law should be passed preventing referendum repeats for 20 years after the first.

However, he said that this law should not be made to look like a “knee-jerk response to a pro-independence majority” in Scotland. As such, he said the Tories should wait until 2022 or 2023 to bring it in.

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Graham, who served as the Member of Parliament for Ochil and South Perthshire from 2017 to 2019, also said that the law should say that referenda can only be held in certain circumstances.

The National:

He suggested one of these would be a party winning a majority with a manifesto pledge to hold one.

Graham said: “A precedent was created with David Cameron that, if you get a majority in the Scottish Parliament who say they want to break away from the UK then you should have a referendum, and that has obviously set us on a particular path.”

The former Tory MP’s admission here that the UK has “obviously” been set on a path towards indyref2 echoes the news that former Scottish Conservative communications chief Andy MacIver (below) says Tories privately admit there is a mandate for a new independence referendum.

The National: Andy Maciver is now a political commentator and director of the public relations firm Message Matters

Speaking to the Scottish Daily Mail, Graham went on: “It would be better to articulate exactly when these things happen and who is involved.

“The Scottish Parliament have obviously passed draft legislation to try to define their own mandate and way to hold referenda elections and I think it would be good for Westminster to update that again.

“We need to be quite careful though that you don’t fall into the trap of looking like you are moving the goalposts deliberately.

“So timing of this needs to be very carefully thought through so it doesn’t look like we’ve got a knee-jerk response to a pro-independence majority.”

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Despite Graham’s plan, one of the underlying constitutional principles of the United Kingdom is that of parliamentary sovereignty. The Government’s own website calls it “the most important part of the UK constitution”.

This principle states that the Westminster Parliament is the supreme legal authority in the UK. There is no existing law which a current parliament cannot undo, and no parliament can create a law which future parliaments cannot undo.

This means that, if Boris Johnson’s Tories were to create a law limiting referenda to once every 20 years, this would only last until a new parliament chose to hold a referendum.

There is no way of stopping a future parliament from doing so without changing the principle of parliamentary sovereignty.

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It is Westminster’s reluctance to countenance any change to this principle that constitution expert Professor Ciaran Martin says means a federal UK would “realistically” never happen.

Articulating this argument, ITV’s Europe Editor James Mates tweeted: “This is all well and good. Except that whenever a Govt wants a referendum, Westminster legislation can simply undo Westminster legislation.

“Unless/until we have a codified constitution, ‘passing a law’ is meaningless.”

Nevertheless, Graham’s proposal has been met enthusiastically by other Unionists, including former Tory development secretary Rory Stewart.

He tweeted: “The basic principle that referenda should be rare and confined to the most fundamental constitutional principles is good. And it seems a very good idea to not get into the habit of asking the same question again and again. Well done @LukeGrahamUK.”