The first obstacle to a Federal United Kingdom is the unfortunate acronym. But perhaps a name change would not be necessary – "united" serves for federal in the United States.
The next obstacle is the relative size of England – the "three fleas and an elephant" problem, as former Welsh first minister Rhodri Morgan put it.
In fact, the UK is three fleas, an elephant and a rhinoceros. Everyone forgets about London, with its assembly and executive mayor. That assembly is not legislative or separate to the executive, but the same was true initially of Wales. London’s status is now being matched by “city deals” across Britain.
The final obstacle is a jealous Westminster, presiding over what is still the developed world's most centralised state. Central government raises 95 per cent of UK tax revenue, compared to 87 per cent in France – the second most centralised – or 50 per cent in Canada.
To some extent federalism asks Westminster to make itself redundant. But if the alternative is the UK ceasing to exist, redundancy should seem the better option.
Parliaments
The idea that federalism is inevitable has been building since 1999, when parliaments were established in Edinburgh, Cardiff and Belfast.
The 2014 Scottish independence referendum gave this an urgent twist – break-up was inevitable and only federalism might prevent it.
Conservatives made most of the early running with this. In 2015 the Tory government passed “English Votes for English Laws”, an act with the unfortunate acronym of EVEL, to turn Westminster into a parallel devolved assembly.
This did not impress influential think-tank the Institute of Economic Affairs (IEA), seen as the flame-keeper of Thatcherism. It responded with a proposal for a federal UK that made headlines throughout late 2015.
The IEA vision was for a highly decentralised state, with almost all revenue raised where it was spent, in order to accommodate left and right-wing governments simultaneously. One of its solutions to the English elephant problem was a two-part federation – Scotland and the rest of the UK.
The Brexit vote gave federalism a further boost.
Last month former Labour foreign secretary Lord Owen published proposals based on the German model, with a "federal council" comprising the four UK nations plus eight English cities.
Owen was taking forward cross-party discussions held at Westminster before the EU referendum, and hence not given sufficient urgency because nobody thought Leave would win.
The focus of those discussions, plus Owen’s follow-up, was defusing Scottish nationalism by getting buy-in from the Scottish National Party.
This week the Scottish government cited Owen's paper in its 49-page Brexit plan entitled Scotland's Place in Europe.
The SNP-led administration stopped short of advocating federalism directly because it believes "the constitutional arrangements of England, Wales and Northern Ireland are matters for the people of those countries".
More powers
However, it linked Owen’s paper with Edinburgh’s demand for more powers to cope with Brexit, saying both point to “the need for a fundamental reconsideration of the nature of the UK state”.
The model the SNP is most interested in is the Kingdom of Denmark, a unique form of federation with parts inside and outside the EU.
The Scottish document notes Copenhagen may "sponsor" membership of the European Free Trade Association for the non-EU Faroe Islands, setting a precedent for Scotland remaining in the single market after Brexit.
The SNP and its independence cause are both felt to have peaked, so Scotland's Place in Europe has been greeted as desperate spin.
Prime minister Theresa May immediately damned it with faint politeness – she has no intention of involving the regions in talks with Europe.
But the SNP's implied acceptance of federalism goes beyond Brexit, creating a general survival mechanism for the UK. In the Scotsman newspaper this October, SNP former minister Kenny MacAskill wrote: "Federalism offers a potential route forward for unionists to improve the constitutional settlement and for nationalists to maintain the dream."
In other words, it is a long-term fudge – the British version of a permanent settlement.
Decades of rows
Any grand plans for federalism would themselves inevitably be fudged such is the nature of UK politics. A written constitution would be expected, heralding decades of rows. A new capital would be needed, distinct from the Westminster elephant – can we agree on Liverpool?
And then there is Northern Ireland, with its existing unionist and nationalist settlement. Could we align it with another? Should we even be asked to try? Sinn Féin has just proposed a federal Ireland to align us in the opposite direction.
In its document this week the Scottish government allayed fears of a hard border with England by making reference to Ireland, where the British government has promised a hard border will not be necessary.
Federalism may never come to either side of the Irish sea, but the argument has already arrived.