The SNP's Westminster leader, Ian Blackford, became embroiled in one of those absurdist Twitter storms last week when he retweeted a comment from the Brexit Secretary, Dominic Raab, suggesting that Scotland was just another “region of England”. How dare the Toies efface our beloved nation, fulminated the SNP's man on the green benches in so many words. Unfortunately, the tweet was a hoax, and Mr Raab had never said any such thing. Cue apologies from Mr Blackford and many SNP twitterati who had also been caught out.

I have to say, the Raab tweet looked genuine to me, since the account was spelled correctly and had the blue tick of authenticity. I could easily have been one of those fooled. It is becoming extremely difficult to tell so-called parody accounts from the real thing, now that political mischief-makers are setting traps. No doubt the Russians are behind it. On social media everything is just a click away, and there's no time to check the authenticity of every post that is retweeted and liked. Indeed, it took some hours for various digitally-savvy journalists to establish that the Raab tweet was indeed fake.

However, Blackford needn't have wasted his time recycling fake news last week, since the real thing was happening under his very nose in the Supreme Court hearing on the Continuity Bill. The UK government’s legal counsel, Baron Keen of Elie, may not have said that Scotland was a region of England, but he made absolutely clear that, constitutionally speaking, Holyrood is little more than a regional tier of government. This is because, like the old Strathclyde Region, it “does not exercise any sovereignty” on its own account. In other words, it is entirely a creature of Westminster. It is not a parliament that can in any sense be regarded as federal – as having its own constitutional status. Power devolved is power retained.

Of course, cynics and old-style nationalists have claimed this all along, but it was still mildly shocking to hear it confirmed so baldly in a legal forum. When Westminster wants to get its way, as it does over Brexit, it must be obeyed, because it is the only source of true legal authority and power in the UK. Everything Holyrood does is contingent and reversible. The Sewel Convention, which was supposed to mean that the Scottish parliament had to give its consent before Westminster legislated on devolved matters, has no legal standing. In fact, is not even a convention any more, but a mere “practice”.

All this emerged in the course of what looked like an exercise in cross-examining the legal door after the horse has bolted. The issue before the Supreme Court judges was whether the Scottish government had the legal authority to pass that Continuity Bill back in March, which sought to ensure that powers repatriated from Europe, in devolved areas like agriculture, fisheries and the environment, went directly to Scotland and were not diverted to Westminster where they could be amended or abolished by Theresa May under her executive powers. The UK government insisted that Holyrood had no right to pass this legislation since it strayed into reserved areas like foreign affairs. The Lord Advocate, Lord Woolfe, said it did because it didn't.

But the dispute seemed more than usually academic since the UK government had already railroaded through the power grab changes in June, after that fifteen-minute filibuster by David Lidington during the final stages of the EU Withdrawal Bill. We surely knew then that Holyrood had been put in its place. However, the Supreme Court debate was, perhaps, a missed opportunity to raise again the issue of the Westminster power grab. Since the dramatic walkout of SNP MPs in June, led by Mr Blackford, this issue has rather fallen from public view. We were promised a campaign of parliamentary disruption similar to that mounted by Parnell over Irish Home Rule a century ago. It hasn't happened – at least not yet.

Many Nationalists blame the press for not giving more coverage to the Supreme Court deliberations. But most political journalists are uninterested in constitutional arguments since they think they go over their readers' heads. These legal formulations need to be translated into the language of politics; distilled into their essence and given emotional resonance. That's largely what politics is about, and it is up to politicians to do it.

The brutally frank assessment of devolution's status by Lord Keen was enough ammunition for an assault by the SNP on the overbearing behaviour of the UK government. It was conformation that the promises made since the 2014 referendum about devolution being “entrenched” and inviolable were essentially vacuous, mere platitudes. Moreover, the UK government had deployed legislative jiggery pokery by delaying the Royal Assent to Holyrood's Continuity Bill so that it could get its retaliation, in the form of the EU Withdrawal Bill, on to the statute book first.

Mind you, to be fair to Mr Blackford, it was difficult to get much purchase on the news agenda last week because so much else was going on. Theresa May’s Brexit strategy was collapsing in a heap. Opinion polls showed that her compromise proposals – the “facilitated customs arrangement” or whatever it’s being called this week – has pleased no one, not least the UK voters, who are massively unimpressed. Then on Thursday, the EU negotiator, Michel Barnier, put the tin hat on it by pointing out that May’s plan for Britain to start collecting customs duties on the EU's behalf was a non-starter. The EU can't legally delegate collection of excise revenue to a country that is not a part of the Customs Union. The whole point of a customs union is to have common tariffs for all countries to simplify collection and avoid fraud. The British proposal looks like a smuggler's charter.

Then there is the unresolved question of the Irish backstop. Theresa May said in Belfast, under the guidance of her Democratic Unionist coalition partners, that there could be no separate customs regime for Northern Ireland. In other words, the North couldn't follow the rule book of the EU Customs Union after Brexit as per December's draft agreement. Was she resiling on that agreement, or was this simply more confusion? The prolific Remain tweeter, Lord Adonis, after visiting the province, claimed that the DUP are now angling for a hard border with the Republic to cement their status as part of the UK, and to hell with the Good Friday Agreement.

So, the United Kingdom, at least the diversified, fluid and decentralised multinational state that has emerged over the last forty years under the umbrella of the European Union, is being destabilised. Scotland is being reduced to the status of a region, the Good Friday accords in Northern Ireland are coming unstuck, the UK government is chaotically taking back control. The will to keep the UK together by constitutional innovation is being replaced by a panicky centralism. This may or may not lead to Scottish independence any time soon – don't expect any timetable for a referendum from the First Minister this autumn because there is just too much uncertainty about Brexit. But what is certain is that Britain is becoming a markedly less harmonious community of nations in this long hot summer of indecision.