Monday must have been a historical first. Never before have three of the four “nations” of the United Kingdom jointly demanded freedom to vote for its dissolution. Scotland, Wales and Northern Ireland have lost confidence in England. They declared in Cardiff that the unionist government at Westminster is “coming to an end”.

There was no such Celtic alliance against the Normans, Edward I or Cromwell. Celtic MPs have never formed a voting coalition in parliament. The Victorian Liberal party advanced “home rule for all”, but that was not independence and it got nowhere. Ireland rebelled, but it did so alone. When this eventually succeeded, Britain said good riddance, kept hold of Belfast and continued to centralise power in London.

So this is serious stuff. Yet London politics this week treated the declaration as on a par with the Oxfordshire village of Piddington voting to go it alone to ward off the possibility of asylum seekers being housed nearby.

The UK’s only serious geographical devolution came in 1999. It was half-hearted, mostly decentralising the running of the welfare state. But it surged the vote for Scottish and Welsh separatism and fed rather than abated the cause of independence. We can only imagine if ruling parties in Bavaria or Provence or Sicily had opted for independence from Germany, France or Italy – or if California said it had enough of Donald Trump’s US. The result would be political eruption.

What does the Cardiff “memorandum of understanding” actually mean? The answer is not much in detail. There was advocacy of policy collaboration, as on childcare and economic growth. There were hints of moves towards further devolution, of the sort promised by Andy Burnham. But there was no suggestion of a new Celtic state, a British Celtica. The talks seemed to concentrate on self-determination, which Burnham had described as “off limits”, at........

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