GORDON Brown has admitted that the independence campaign is stronger than Unionism.

In a major intervention in the constitutional debate, the former Labour prime minister warned Unionists of the need for a “positive argument” if they wanted to keep the United Kingdom together.

It is a significant admission from Brown, who was instrumental in the Better Together campaign against independence in 2014 – sometimes dubbed “project fear” by the Yes side.

Ultimately Brown’s side won out – but support for independence remains high in Scotland, with a number of polls giving  it a lead over the Union in recent months.

And he admitted that just because the SNP have “messed up”, in reference to their flagging performance in opinion polls, that did not mean independence was off the table.

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Speaking to the Financial Times, Brown said that “support for independence has remained exactly the same” despite the SNP’s dwindling fortunes.

He added: “You’ve got to put a positive argument. You can’t just say the SNP have failed, therefore independence is off the agenda ...

"In the long run, the forces pulling Britain apart are greater than the forces holding it together, unless something is done about it.”

Brown’s comments are also significant as he is the author of a constitutional report commissioned by the Labour Party.

The report offered some new powers for Holyrood and the headline proposal of abolishing the House of Lords – the possibility of which the Labour leadership have played down.

Critics called the document “spectacularly underwhelming”.

Keith Brown, the SNP's deputy leader, said: “There has never been a positive argument for Scotland remaining under Westminster control and it seems that even Gordon Brown can now see that to be the case.

“During the 2014 independence referendum, the 'No’ campaign was built on nothing more than scaremongering and, what we can now see to be, broken promises - and, since then, the damage Westminster has inflicted on Scotland is unforgivable. 

"Westminster isn’t working for Scotland and there is no positive case for broken Brexit Britain - only the SNP and independence offers a better future for our country.

Scottish Greens MSP Maggie Chapman said: “The problem with Gordon Brown’s latest intervention is the fact he failed to reform the electoral system when he had the chance, failed to ensure Scotland’s best interests were taken into account, and failed to prevent the Tories getting into Downing Street for which we are now all paying the price.

“Given opinion polls shows public opinion on independence is broadly 50-50 at the moment, way higher than when the Yes campaign first kicked-off, and after more than a decade of Tory austerity, any new Labour government must accept Scotland deserves the chance to put a vote to the people once again - anything less would be undemocratic. 

“This weekend thousands of people will gather in Glasgow again to show their support for independence. Labour cannot ignore the will of the people the same way as the Tories continue to do, and it seems even Gordon Brown can recognise that.”