The UK risks becoming a "failed state" unless it makes reforms to the union, former prime minister Gordon Brown has warned.
Mr Brown urged Prime Minister Boris Johnson to consider ideas like replacing the House of Lords with a "senate of the regions" and to review the way the UK is governed.
It comes after The Sunday Times published the results of opinion polls in the four nations of the UK, which found a majority of voters thought Scotland was likely to be independent in the next 10 years.
In Scotland, the poll found that 49% backed independence compared with 44% against – a margin of 52% to 48% if the undecideds are excluded.
Writing in The Daily Telegraph, Mr Brown said that "the choice is now between a reformed state and a failed state".
He called on the Prime Minister to set up a commission on democracy which would review how the UK is governed.
Mr Brown writes: "The commission will discover that the United Kingdom urgently needs a forum of the nations and regions that brings them and Boris Johnson together on a regular basis.
"No country can have national integration without political inclusion, and the commission might start by learning from the experience of countries like Australia, Canada, Germany and America where, partly because of British influence in times past, second chambers are senates of their regions, and minorities who can easily be outvoted are guaranteed a stronger voice."
Mr Brown also said that the Prime Minister should use the Armed Forces and the NHS to demonstrate the "everyday benefits" of the union.
The Sunday Times poll found that in Northern Ireland, 47% still want to remain in the UK, with 42% in favour of a United Ireland and a significant proportion – 11% – undecided.
However, asked if they supported a referendum on a United Ireland within the next five years, 51% said yes compared with 44% who were against.
In Wales, where support for independence is traditionally weakest, 23% still backed leaving the UK while 31% supported a referendum.