NEVER has so much of our lives depended so crucially on seemingly so little; a single letter: R.

The R rate, which relates to the reproduction of the monster coronavirus, will dominate the country’s mind in the coming weeks and months.

And, in particular, that our national resolve can keep R well below one. Anything above this will spell disaster as the transmission would lead to a second wave, the NHS being overwhelmed and the economy tanking.

A troublesome aspect is that the level is not the same across the UK. It is, for example, suggested that in Scotland it is somewhere between 0.7 and 1.0 while in England it is between 0.5 and 0.9. In London, it is thought to be even lower, between 0.5 and 0.7.

Given health is devolved, it is easy to see that lifting a restriction on one side of the border might not be so prudent on the other, which can, of course, lead to a whole range of political and social complications.

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It has been suggested reopening schools could add 0.2 to the level; hence, perhaps, Nicola Sturgeon’s reluctance to see any school reopening in Scotland any time soon.

Indeed, she has made clear unlocking "must go at the pace of the part of the UK that is furthest behind in the infection curve” ie Scotland. In a warning to Boris Johnson, the First Minister told him in no uncertain terms that she was “not prepared to countenance” any other approach.

The frosty relations between the two leaders dipped a few degrees lower when an understandably angry Ms Sturgeon decried the raft of newspaper reports outlining how “freedom day” would begin on Monday and people could prepare to picnic, ramble, play tennis and golf in the great Covid-free outdoors. The suspicion was Whitehall’s, and possibly even Downing St’s, fingerprints were all over the briefings.

Ms Sturgeon warned her colleague sitting in No 10 that any idea, as mooted, of dropping the stay at home message, could be a “potentially catastrophic mistake”.

No 10 was keen to stress how the PM had told Cabinet the Government would “advance with maximum caution” in loosening any lockdown measures. It insisted the stay at home slogan would remain a “core part of the messaging”.

The two leaders yesterday afternoon exchanged pleasantries on the phone in a "constructive" half-hour phonecall.

They are set for a rematch on Sunday at the Cobra emergency meeting, which will take place alongside yet another virtual Cabinet, which will sign off the phase two strategy based on the latest advice from the expert SAGE group.

However, it is clear serious cross-border strains are beginning to appear as the PM wants to press his foot on the mushroom, as they say in France, while the FM is keen to yank on the handbrake.

No 10 told me that “modest” divergences were possible but would have to be rooted in scientific evidence.

Yet one can only imagine the political and social fall-out if some restrictions were lifted in England but maintained in Scotland.

Fearful folk south of the border would question the wisdom of easing measures when north of the border they were not being lifted. And, equally, some in Scotland might think if people in England can sit in cafes and beer gardens why can’t they.

However, for all our sakes, the two leaders really need to sort themselves out and rise above the natural well of political distrust and animosity that exists between them in order not to fuel public fear. The time calls for statesmanship to help save lives.

So, come Sunday night, the PM’s presentation is likely to be high on rhetoric but low on substance. The handbrake is likely still to be firmly on.

Mr Johnson’s televised address to the nation will focus on easing social distancing measures to help more small shops, garden centres and offices begin the slow crawl to normality.

READ MORE: Nicola Sturgeon warns Boris Johnson over 'potentially catastrophic' message change

Given the transmission rate of Covid-19 is less outside than in, then some outdoor activities could be relaxed; a little. So, we could see people picnicking in parks and rambling on hillsides but still strictly maintaining the two-metre rule.

Alongside these, it seems clear now wearing face coverings on public transport and in shops will become the order of the day.

A document to accompany the PM’s speech will set out "milestones" and is expected to set out timelines of what we might be able to begin doing again should the R rate be kept under control and when.

Of course, a large part of the PM’s Sunday evening presentation will be about striking the right balance between beginning the great “unlockdown” and saving as much of the economy as possible.

This is one of the trickiest elements of all in the battle against the coronavirus; how and when, for example, to ease back on the furlough and mortgage holiday schemes. None of this is easy.

This week, Dominic Raab has sought to reassure us that “there is light at the end of the tunnel”.

We can only hope the national resolve will eventually lead us into the daylight and that the light the Foreign Secretary speaks of is not attached to another coronavirus express.