Gordon Brown has called for sweeping constitutional changes including a “council of the north” to avoid the break-up of the United Kingdom.
The former prime minister criticised what he called “cosmetic gestures” by Boris Johnson, who has suggested moving the House of Lords to York in a bid to burst the Westminster bubble.
But Mr Brown said there must be more done to keep the Union together after Brexit.
Speaking to Sky News before a speech at a Hope Not Hate event, Mr Brown said: “I think getting Brexit done is in danger of leaving Britain undone.
“We have got to face up to the fact that unless we fundamentally change our constitution, Scotland may succeed from it and the regions will feel uncomfortable within it.
“Boris Johnson can’t just have cosmetic measures like moving the House of Lords, there has got to be substantive change.
“People are very fed up with stagnant wages, public services which are deteriorating, boarded up town centres. The regions and nations must have a voice.”
He is proposing a “forum of the regions and nations and a council of the north” as well as a council for the Midlands, and funding for each in the same way as Wales and Scotland.
Mr Brown added: “This is a sort of constitutional revolution. We have been a unitary state for too long, once we bring in nations and regions you have a very different kind of UK and Scotland, Wales and Northern Ireland would feel more comfortable.”
He said the UK will be under pressure to change the constitution and said Scotland could feel more comfortable in a United Kingdom which reallocates resources to outlying nations and regions.
Mr Brown, a staunch opponent of Scottish independence, denied that there was a need for a second Scottish referendum.
He said the Scottish Parliament leader’s “two arguments” had not been met.
He said: “We don’t know the future relationship with Europe yet and the other was a consistent majority of support for independence and there is no such case for it yet.
“It’s a divided Scotland.”
He also criticised Ms Sturgeon for not using all the powers available to her party but said they should get more after Brexit.
He said: “Extra powers have gone to the Scottish parliament and I believe after Brexit there will have to be additional powers go to the Scottish parliament – fishing, farming have been transferred to Whitehall and they should go on to Wales, Scotland, Northern Ireland and the regions.
“The Scottish Parliament has the power to top up benefits but they haven’t used them.
“The Scottish government needs to do more.”
Mr Brown said Mr Johnson would have to answer for his claims that there would not be a border in the sea between Northern Ireland and Great Britain and said the solution offered by the current prime minister is a “justifiable source of grievance” for Northern Ireland.
Meanwhile, he refused to criticise the rising costs of HS2 outright but did say it would make more sense if it was “going right to the north in the end and going to bring the whole country together”.
He said: “We need a transport plan for the future infrastructure of the UK, so much has been spent on London on Crossrail, and for the Olympics and the north was neglected.
“The plan has got to improve what happens in the North East.”
Mr Brown did not disclose who he is supporting to replace Jeremy Corbyn in the Labour leadership race but indicated he would choose a candidate to back when the final names make it onto the ballot paper.