In my most recent column, I raised the question of whether or not the thus-far successful effort to keep the different parts of the UK moving in tandem on Covid-19 might founder.

The danger was twofold. First, after weeks of chronicling various ways in which Holyrood and Cardiff Bay had made a point of doing things differently where they felt they could get away with it, it seemed likely that this devocrat reflex might take over once the exigencies of the crisis started to ease.

Second, despite shortcomings on the part of both the national and devolved governments it appeared that Wales, for example, might simply not have the policies and infrastructure in place to move on to the next phase at the same time as England. (Scotland too is struggling to get testing up.)

Well, the Prime Minister broadcast his message about easing lockdown yesterday and lo and behold, cracks are appearing in the so-called ‘Four Nations’ approach, with both Cardiff, Belfast, and Edinburgh disavowing the shift from ‘Stay Home’ to ‘Stay Alert’. And in fairness to them it appears that they (like the Cabinet) were shut out of the decision, only learning of it after it was briefed to journalists.

It’s easy to over-interpret the current gap in policy terms: despite the different slogans, both London and Edinburgh have announced a few new liberties within an ongoing injunction to stay home as much as possible.

But there are evident tensions. For example, Wales has not matched the Government’s decision to allow people to drive elsewhere to exercise, and this has led to Welsh ministers to state that: “Our regulations do not permit people to get in their cars and drive to destinations in Wales and this includes people getting in their cars in England.”

The prospect of cross-border movement restrictions inside the UK – some Scottish nationalists have also been calling for the border to be policed – is just one potentially troubling outcome.

Another is the idea that the Treasury, and by extension British taxpayers, might be expected to continue to subsidise expensive economic interventions such as furlough in Scotland and Wales without having a say on how these nations leave lockdown. It is all very well for Mark Drakeford to talk about “maximum caution”, but it isn’t his government that will foot the bill.

Alternatively, central Treasury decisions to reduce such schemes could be seen as strong-arming the devolved administrations, a battle the Government would need to be prepared for. It is certainly reasonable to make UK economic and financial support conditional on a coordinated UK response – ‘British cash with British strings’, if you like – but it will anger those who subscribe to an entirely one-way interpretation of the ‘devolution settlement’.

Even if such fraught constitutional battles don’t immediately break out, there are evident dangers both that mixed messaging will undermine efforts to stem fraying public obedience – especially in Wales, where the now-Parliament enjoys a rather low profile – and increase temptation to travel in order to exploit differences in approach.

Either way, the pandemic has exposed more clearly than ever what already ought to have been evident: that intergovernmental cooperation cannot effectively replace Westminster when authority needs to be exercised on a nationwide level – that a ‘four nations’ approach is no substitute for a ‘one nation’ one. Where a British response is needed, the British Government should provide it.