IT was a month before the independence referendum when Gordon Brown let rip with the F word. The constitutional F word, that is.

Addressing an audience at the Edinburgh International Book Festival, he said: "We’re going to be, within a year or two, as close to a federal state as you can be in a country where one nation is 85 per cent of the population."

It wasn't the first time he had spoken of a "near-federal" UK but this was the moment it became clear the idea was at the very heart of his case for Scotland staying in the UK.

His vision was of a series of national parliaments and regional assemblies across the UK each with its own suite of economic and tax powers. A senate of the nations and regions would replace the House of Lords.

The former prime minister continued to hammer the message in the weeks before the referendum.

"It's like home rule in the UK," he declared during one speech at a former miners' club near Edinburgh.

Since the referendum, Mr Brown's comments have been used repeatedly by the SNP to support its claim the Scotland Bill has fallen short of expectations.

Alex Salmond went so far as to suggest that voters would be so angered by the new legislation's failure to deliver a federal constitution it would trigger a second independence referendum.

That seems unlikely. Federalism remains a minority interest though, interestingly, support for it can be found across the political spectrum.

The Lib Dems have long been advocates and a Labour Campaign for Federalism is - albeit slowly - getting off the ground. There are even some Nationalists who see a federal UK as a sensible staging post on a gradual journey to independence.

As it happens, Mr Brown was not among those arguing for full-blown federalism. His careful remarks (never quoted in full by the SNP) explained the problem: one part of the UK accounts for 85 per cent of its population. Federations are rarely if ever so lop-sided.

For those who like the idea, the difficulty has always been England.

Ever since John Prescott's failed attempt to deliver assemblies and elected mayors in the 1990s, it has been assumed there is no real appetite for regional devolution. Recent research by Cardiff University appeared to confirm the view. It showed that no matter how dissatisfied with their governance the English might feel, regional assemblies are the least popular solution. They are less popular than an English parliament, which is much less popular than English Votes for English laws.

A non-starter, then? Perhaps not. Last week a small group of voters in Sheffield took part in what was billed as a "citizen's assembly" to debate and vote on regional devolution. The exercise was organised by Democracy Matters, a group of academics from four universities and the Electoral Reform Society, funded by the Economic and Social Research Council. It is designed to find out what people think when they engage more deeply with the issue.

To that end, the South Yorkshire guinea pigs spent two weekends hearing from the likes of Lord David Blunkett, local MPs, council leaders, senior officials, constitutional experts and campaigners.

At the end of it all, they

backed calls for a Yorkshire and Humberside regional assembly, with tax-raising and legislative powers.

On the face of it, the result was surprising. As recently as three years ago, the people of Sheffield voted by two to one against having a directly elected mayor run their city.

But the regional assembly option proved more popular than an existing plan - the latest part of George Osborne's Northern Powerhouse initiative - to create a Sheffield city region with new cash and powers, spanning nine local authority areas in Yorkshire, Nottinghamshire and Derbyshire.

The Democracy Matters panel voted to reject the £900million city deal and instead press for a much wider assembly that would deliver stronger powers over transport, economic development and education.

"It's not that members of our citizen's assembly did not want devolution," said Professor Matthew Flinders, who headed the project. "What they want is genuine devolution with stronger powers and more accountability."

If the UK has a federal future, it remains a long way off. But moves towards a looser constitutional settlement are not completely dead in the water. Scotland has long acknowledged that devolution is a process not an event. Maybe England's new city regions will discover that too.