Boris Johnson is being urged to allow Scots living anywhere in the UK to vote in a second independence referendum.

Cabinet members are thought to pushing the Prime Minister to toughen up rules around a potential second vote in a bid to save the Union. 

The prime minister is also being urged to appoint Ruth Davidson, the former Scottish Conservative leader, to a newly created role of constitutional secretary, making her nominal head of the pro-Union campaign.

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One cabinet minister told The Times: “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. The other is to bring Ruth back into the front line. She is the best pro-Union voice we have.”

Another senior Tory figure told the paper: “Independence is behind in the polls now, and Sturgeon is getting flak from her own side for not talking about it since the election. We need to get out there on the front foot and start acting like we’re ahead and not just wait for her to catch up again, which was the catastrophic mistake we made after the 2014 referendum.”

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The "Union Unit" set up to bolster support for the Union has lost two leaders in the past year and its role has now been passed to a cabinet committee. With Michael Gove, the Cabinet Office minister, now focusing on the Covid-19 recovery, there is no single senior government figure in charge of the defence of the Union.

800,000 people who were born in Scotland now live in England and up to 50,000 live in Wales, with the majority estimated to be pro-Union.

Polling expert, Sir John Curtice, has previously calculated that the inclusion of Scots living elsewhere would swing the vote against independence if Scottish voters in Scotland did not get over 54% of the vote.

Ruth Davidson stood down as an MSP at the Holyrood elections last month and has been nominated for a peerage. She told The Times that she would not rule out a ministerial job in future, but indicated the time was not yet right.

Tentative plans for a cabinet reshuffle in July have been abandoned by No 10 because of the pandemic.