Just how much does Boris Johnson value the Union? Well, about £60bn at the last count. Last week, the Prime Minister effectively bounced his Chancellor, Rishi Sunak, into extending the costly furlough scheme until March 2021 by announcing that it would be available whenever Nicola Sturgeon asked for it.

The new Scottish Tory leader, Douglas Ross MP, had his first major win. He had asked the PM in parliament on Monday to disprove the SNP's claim that “an English job is more important than a Scottish one”. He secured an open-ended commitment from the PM that Scotland would have furlough cash irrespective of whether England was locked down or not.

This blind-sided SNP MPs who at first couldn't believe their ears. Nor could many Conservative MPs. Indeed, on Tuesday morning, Robert Jenrick, the UK Communities Secretary, was still telling BBC radio that any extension of the furlough scheme beyond the 2nd December cut off “was a matter for the Chancellor”. In other words, that it was at Rishi Sunak's discretion. It wasn’t.

It took a couple of days before Mr Sunak formally announced in parliament that scheme paying laid off workers 80% of their wages would now last until March – fully a year after furlough began. This was the big bazooka – a blast of borrowed cash that will add at least another £60 billion to the Covid bill. And that isn't counting the extra £1bn for Scotland also announced last week to meet contingent costs.

We've never seen anything like this. The monetary spigots have been opened with a vengeance. The Bank of England announced another £150bn of money printing, or “quantitative easing”, last week to ensure that the government didn't go bankrupt this winter. What happens thereafter is another matter. Boris Johnson believes the pandemic will be defeated by Spring and that the future can look after itself.

His Chancellor had wanted to end furlough well before that. He'd planned to replace it with his cheaper Job Support Scheme. So this looked rather like Number Ten taking back control. The PM is perhaps fed up being upstaged by “dishi Rishi” and wants to be seen as Mr Giveaway too – even though many Tories, as well as the Institute for Fiscal Studies, think this extension is a reckless use of public money.

But what above all prompted last week's dramatic intervention was the threat to the Union. Boris Johnson is fully aware of how unpopular he is in Scotland. He's seen those opinion polls – nine of them – showing that a majority of Scots now favour independence. He had to stop Nicola Sturgeon claiming Scotland only got furlough cash when England was on lockdown. Hence his choreographed parliamentary exchange with Douglas Ross.

We have become used to U-turns from birling Boris, on face masks, exams, working from home, extending school meals and the lockdown itself. Less than two weeks ago, Mr Johnson was accusing the Labour leader, Keir Starmer, of “opportunism” over his call for a circuit-breaker. Now he has one which looks open-ended and costing more than Jeremy Corbyn ever dreamed of.

It is a desperate move by a PM living on borrowed time. Having delayed lockdown when his medical advisers called for one, Mr Johnson left himself exposed. Covid deaths will rise inexorably in the countdown to Christmas, like some morbid advent calendar, and Labour will try to hang every one of them around his neck. An early circuit-breaker “could have saved thousands of lives” according to Professor Andrew Hayward of SAGE on BBC's Today programme this week. No prime minister can survive that.

Mind you, Nicola Sturgeon is not entirely immune to criticism here. By focusing on the money and confusion, the Scottish Government neatly avoided awkward questions about why Scotland also ignored the SAGE advice to impose a full lockdown. Moreover, at her briefing last Monday, she suggested she might introduce one just to get furlough cash. “Should we take the opportunity of more generous financial support,” she asked herself, “ to step harder on the brakes now?” I'm not sure that's what is meant by “following the science”.

The call for a lockdown, made by the UK scientific advisers in late September, was not specifically directed at Scotland, and infections were still low here – but infections were relatively low in England too. Wales took the SAGE advice seriously and went down the lockdown route. Nicola Sturgeon opted for a local approach, similar to England's three-level system, except with more tiers – though she is now threatening a travel ban by law.

I'm not saying that the First Minister was wrong to avoid lockdown. The human costs are huge. And it may well be that the Scottish approach is vindicated in practice since Covid cases appear to be tailing off here without any lockdown. That is unalloyed good news. If the second wave is indeed past its peak, there could now be light at the end of the Covid tunnel.

The mass testing of the entire population of Liverpool is under way, and we can only hope that this works rather better than the apps and the dodgy testing kits. The pressure will be on for the Scottish government to introduce mass screening in similar hotspot areas like North Lanarkshire. Liverpool is the realisation of the Mass Population Testing Programme, which Boris Johnson dubbed “Operation Moonshot” in September. It is a potentially £100bn programme to test the entire population of the UK on a regular basis. It has to be continuing because a test only says you don't have the disease today and tells us nothing about the likelihood of catching it tomorrow.

As in wartime, governments are always looking for the magic formula, the secret weapon, the game-changer that turns the tide – or whatever mixed metaphor comes readily to hand. This time it may be that the moonshot is, like Apollo 11, finally on course. Mr Johnson will claim credit for the Union. The tests are quick and simple and have, we're told, only a one-in-1,000 false positive rate. That is low enough for those cases to be re-tested in a lab.

Government advisers say this will allow the quarantine time to be reduced from two weeks to one, ensuring much wider compliance. Of course, that assumes enough of us will be happy to take the test. A YouGov poll in July suggested that one in five in the UK may refuse a vaccine if and when it becomes available. A combination of government incompetence and public resistance could still throw the moonshot off-course. But there is also increasing confidence among scientists that a vaccine will be available in the spring. It will take months to produce it in scale.

With mass testing and a vaccine for at-risk groups like the elderly, that much-maligned herd immunity might finally become a reality. This may indeed be the end of the beginning of the fight against Covid. But it still looks like the beginning of the end for Boris Johnson.