Constitutional marriages can be delicate things, having to resist constant pressures from within and without. Which perhaps makes it all the more remarkable that the one between Scotland and England has lasted for more than three centuries. But are the divorce lawyers now preparing their briefs? Last week, Mark Drakeford warned the Union had never been so fragile and change was needed urgently or the “case for the break-up of the UK will only increase”. Music, no doubt, to Nicola Sturgeon’s ears. The Wales First Minister produced a 20-point plan to improve devolution and see the constitutional marriage survive into the future.