DIFFERENTIATION is a key effect of devolution; different parts of a country doing things in their own way.

The approach to the coronavirus has underscored this across the UK for much of the time of the pandemic, although this week we saw a coming together to adopt a four nations’ strategy to Christmas; albeit for just five days.

Yet the political reality of the past few months has been how approaches to health for millions of people have been anchored in Edinburgh, Cardiff and Belfast and not in London. Indeed, at times the regions of England have spoken up for more distinctive localised policies and against what they see as Whitehall diktat.

Yesterday, we saw sparks fly over the UK Government’s “authoritarian” decisions on tiers for England, which could have a major bearing on who travels where over the festive period.

While Covid-19 is having an impact on all our lives from a health, social and financial aspect, it is also having one politically. The virus, and the different ways each of the four nations is tackling it, is feeding into the constitutional question and shaking the ground beneath Unionist feet.

Last week, Douglas Alexander, the former Labour Scottish Secretary, reflected on the creation of the Scottish Parliament, explaining how the aim had been to build a “workshop for social justice more than a totem of national identity”.

He decried how Holyrood had “prioritised symbolism over substance” but accepted the rise in “identity politics” had become a dominant force few would have imagined in 1999.

Nicola Sturgeon has regularly insisted that the pursuit of a different approach to the pandemic than Boris Johnson’s has been driven by Scottish circumstances on the ground rather than any political quest for differentiation.

And yet it is obvious that when voters see a national leader day in and day out pursuing a devolved approach to a key issue, they become ever more used to differentiation and this gradually feeds into the constitutional debate.

Is it coincidence that, as the first UKwide lockdown began, a poll had the pro-Union vote just ahead but ever since, as the four nations battled the virus, the pro-independence vote has gained the upper hand? Earlier this month, a snapshot gave it a strong 11 per cent lead.

Since 1999, there has been what one MP branded “devo-creep,” the devolved administrations gradually gaining more powers with new acts of the UK Parliament. Of course, it is a natural process; if you create a new parliament, over time it will want more powers. The Welsh executive and assembly have become the Welsh Government and Senedd.

Ever since Lord Robertson uttered that notorious line of "devolution killing Nationalism stone-dead,” the pro-Unionist cause has struggled to draw a line in the sand on how much power should be devolved beyond the centre.

The Whitehall view in giving the Scottish Parliament more control over taxes in Scotland was to increase the accountability of Edinburgh ie MSPs could hardly continue to blame London if they had more power over their finances.

The Conservative argument goes that Nicola Sturgeon and her colleagues only believe in devolution as a means to an end: independence. They are not true believers.

Of late, there has been an almighty ding-dong over the UK Internal Market Bill with the First Minister branding it an “abomination,” a naked power-grab by Westminster that undermines devolution while Michael Gove, the Cabinet Office Minister, insists it will provide Scotland with a post-Brexit “power surge” and so boost devolution.

Interestingly, responding to the Spending Review, Alister Jack pointed out how the UK Government would use the new post-Brexit UK structural fund to liaise directly with local councils ie bypass Holyrood. This, asserted the Scottish Secretary, was “real devolution”.

The Prime Minister’s recent devolution-has-been-a-disaster-in-Scotland gaffe has been an early Christmas present to his opponents, who will use it every day until polling day to score a political point.

The fact Boris goes down like a lead balloon for much of Scotland is not lost on Scottish Conservative minds; to maximise the Tory vote next May, Douglas Ross is pursuing his own differentiation policy - from the PM.

But the Unionist campaign is clearly wobbling. John Major’s two-referendums proposal had his colleagues shaking their heads; how did he think people would vote in the first poll? A Yes vote would change the constitutional ground forever.

Another Tory grandee Sir Malcolm Rifkind argues the current devolved settlement is nearing its sell-by date and has become another voice advocating federalism to save the Union.

But has the constitutional tide turned for good?

As the waters rise ever higher will the PM be able to maintain his “just say no” to indyref2 position or will he be become a modern day King Canute, urging the waters to go back only to be engulfed by a tsunami of differentiation.