Nicola Sturgeon with her Brexit minister, Michael Russell. She said that Scotland’s strong ”no” vote in the EU referendum means it should be given another chance to leave the UK

Theresa May is preparing for the Scottish government to call a second independence referendum to coincide with the triggering of Article 50 next month.

Senior government sources say there is serious concern that Nicola Sturgeon will use the start of the Brexit process to demand another vote on the future of the UK and that Whitehall is planning for that event.

Sturgeon makes her case for IndyRef2

The prime minister could reject the demand, but such a move would risk causing a constitutional crisis. If she agreed, ministers have been warned, she would risk the break-up of the United Kingdom on a “coin toss”.

Mrs May has also been told that she faces a double-headed “devolution crisis” next month, with Stormont elections on Friday unlikely to resolve Northern Ireland’s political turmoil.