The leaders of Scotland, Wales and Northern Ireland will gather on Monday to sign a deal designed to kick-start the break-up of the United Kingdom, The Telegraph can disclose.

At an unprecedented summit in Cardiff, the three first ministers will put pen to paper on a joint declaration demanding the right to hold independence referendums.

Mr Swinney said on Sunday: “For the first time ever, Scotland, Wales and Northern Ireland are led by pro-independence first ministers. There could be no clearer sign that the status quo is not sustainable – and that Westminster must prepare for a post-UK future.