As posturing over Brexit has given way to negotiations, the European Court of Justice is looming large. The prospects for EU citizens resident in the UK, uncertain enough to begin with, have been obscured by the government’s insistence that ECJ judges won’t be determining their rights. Even the court’s regulatory role over nuclear research is one judicial pretension too many for London: Theresa May has committed the UK to withdrawing from the European Atomic Energy Community as well as the EU, because the ECJ sorts out Euratom disputes.

May’s inflexibility is consistent, for what that’s worth. In her first detailed speech on Brexit, delivered to the Tory conference last October, she put ECJ jurisdiction on a par with immigration as issues on which there would be no compromise. This was reiterated in a White Paper. But the undertaking raised a question that has grown only more pressing. It came at a time when ministers were saying little else about Brexit, ostensibly because silence was a clever negotiating tactic. What made the government object so unequivocally to the Luxembourg court?

Having backed the status quo during the referendum campaign, May was keen to prove her newfound opposition to the EU. It seemed wise to placate, or at least wrong-foot, colleagues with better Brexit credentials. They included the man she duly elevated to foreign secretary – and it is largely thanks to Boris Johnson that the ECJ assumed such significance.

Like any effective politician, Johnson knows the value of simple themes, and while other Brexiters spent the referendum warning against immigrants or promising a free-trade bonanza, it was the villainy of Luxembourg’s judges that bothered him from the start. He flagged them up as a threat when he announced his conversion to Brexit in February 2016 – condemning the ‘single unified judicial order’ they sought to impose – and over the next three months, in the Telegraph, on the Andrew Marr Show and on the stage of Wembley Arena, he condemned the court for facilitating ‘legal colonisation’ by the EU.

Johnson is no jurist and his critique drew heavily on a detailed argument that his wife, now a QC, published shortly before his February proclamation. But his stance – essentially, that a country’s sovereignty is diminished whenever it accepts the authority of a transnational tribunal – has been shaping government policy ever since. Its most important consequence so far has involved the Charter of Fundamental Rights, the EU’s more expansive version of the European Convention on Human Rights. Answering some unusually precise complaints made by Johnson, the government is going to deny the charter legal force from the moment the UK leaves the EU – instantaneous oblivion that won’t befall any other EU-derived legislation. It’s conceivable that Johnson isn’t responsible. But there are no lawyers of distinction left in the Cabinet, and though David Davis no longer pretends to be a maverick, he once respected the charter enough to challenge UK data-retention powers before the European Court of Justice.

It’s unlikely to end with ditching the charter. A scorn for judges plays well among Brexit audiences, and disliking continentals is perennially popular. The usual target wasn’t historically the ECJ – it was the European Court of Human Rights, which is independent of the EU – but your average Europhobe doesn’t distinguish between cross-Channel legal interferences. And ministers have incentives to exploit the anti-legal sentiment. So few principles separate the Brexiter challengers to May that it could spiral.

That would be bad. Although the European Court of Justice does indeed interfere with some governmental actions, oversight is important even when conducted by foreigners – as David Davis might once have testified. ‘Sovereignty’, meanwhile, is a nebulous concept – signifying a concern with power, but identifying no safeguards to prevent its abuse – and while nationalists may like the idea of a country that does just what it wants, democracy demands checks and balances.

Repudiation of the ECJ isn’t really about ‘taking back control of our laws’. It’s a centralising measure by a government that lacks confidence in its arguments: part of a process that has seen it also try to deny Parliament and the Supreme Court their proper supervisory role over Brexit. In the name of abstract sovereignty, the rule of law and the separation of powers are being jeopardised. It’s a sorry picture, indicative of an executive that lacks a legal soul, and as May’s rivals jostle for advantage, their two-bit theorising to justify the dismantling of rights could wreak far worse damage. They’re out to take all the control they can grab.