When the horses line up for the Cheltenham Gold Cup this afternoon, it would be astonishing to learn that Theresa May had her feet up and was watching the race on television. Still less that she had put a pot of her money on a well-priced outsider.

Although May has been remarkably fortunate in her political career, and has ridden her luck with great nerve, she never gives the impression of loving a flutter. This week, adopting her most withering tone as she did it, she stressed once again her belief that “politics is not a game”.

You can read right through Rosa Prince’s recent biography of May and find no hint whatever of the fact that our prime minister has a gambling problem. On the contrary. The things people say about May draw an entirely different picture. She is hardworking. She gets on with the job. She is a safe pair of hands.

Yet the striking truth about May is that she has become one of the biggest risk takers in modern British politics. Not only has she staked her entire premiership on delivering the hard Brexit she thinks the voters will back; now she has also bet the farm that Nicola Sturgeon’s SNP won’t win the support to take Scotland out of the UK in a second independence referendum too.

It can’t be stressed too much that this is all seriously odds-defying stuff. To put the bulk of the British economy in hazard over Brexit would be a big enough punt for most politicians. But by eyeballing Sturgeon across the green baize table, May is now more or less daring the Scottish first minister to try to break up the UK. She had better know what she’s doing is all I can say. For her prime ministership has now embarked upon a spring double that will lead to either outright triumph or complete disaster.

The first part of May’s gamble is not directly of her own creating. Like most sensible Conservatives, she wanted on balance to remain in Europe. However, when the result went against her she decided that her job was to make Brexit work. She could have done this by going for a soft Brexit that prioritised economic security, as most MPs want. Instead she chose a hard one that put immigration first.

This is a huge gamble in itself. The City doesn’t like the approach. Nor does industry. Nor do the 48% who voted remain. Nor do the soft leavers who worry more about sovereignty or European commission creep. Nor do liberal Tories. Nor do most commentators. Nor does unwilling Scotland, nor both parts of anxious Ireland.

The European Union doesn’t want it either, and it’s the EU with which she must craft terms of exit that don’t wantonly damage the British economy, the cohesion of Europe and Britain’s soft power in the world.

Yet in this government the hard line on hard Brexit trumps everything else, however sensible. The humiliation of Philip Hammond’s attempt to raise national insurance contributions for the self-employed is the latest example. Ordinarily this would have been a policy that May favoured, because it is socially just and fiscally responsible. But the breaking of a pledge undermined public trust, offended too many troublemakers in the party and turned the Daily Mail briefly against her. So it had to go.

Why does May set such store by hard Brexit? The reasons have nothing to do with economic prosperity, social justice or maintaining the UK – all things she cares about. The only logical explanation of her stance is that she believes she will get a deal from Europe that will disarm her liberal critics while not provoking her conservative critics to revolt against her.

If that’s not a gamble, then the word has little meaning. The same goes for the prime minister’s handling of Scotland. Here, though, May is making not one big gamble but three.

The first is that, at a time of May’s choosing, probably in 2019, the Brexit terms offered to Scotland will be sufficiently enticing — further powers devolved from Brussels via Westminster to Holyrood, and perhaps even some form of special economic association with the EU — to disarm Sturgeon. The second is that May will do no damage to the anti-independence case by refusing Sturgeon’s wish for a second referendum vote in 2018-19.

The third, with potentially the highest stakes of the lot, is that if and when there is a second referendum, which the SNP will relentlessly frame as a choice between supporting Scotland and supporting the Tories (ie the English), Scottish voters will astonish themselves and us by choosing the latter not the former.

This isn’t merely a gamble on May’s part. It’s an act of reckless political daring. It’s straight out of Danton’s playbook on boldness – de l’audace, et encore de l’audace, et toujours de l’audace. And look what happened to Danton – he lost his head.

If May’s Scottish gamble comes off – which would mean Scots vote to stay in the UK and to accept the Brexit terms, while delivering a possibly mortal wound to the SNP in the process – the Tories will be beside themselves with delight. If it fails, May will have engineered the breakup of the United Kingdom after 300 years, precipitated a new Irish confrontation after 20 years of peace, created a crisis over Trident, and fast-tracked the loss of the UK’s UN security council seat.

It’s possible that May will triumph on all fronts. That outcome can’t be ruled out. For it to happen, however, the hard Brexit language of today and the dismissal of Sturgeon’s demands will have to turn out to be opening bids that conceal a much more pragmatic and consensual May than she has publicly revealed. Is that all part of the game plan? Perhaps. But there is no evidence for it yet.

And yet, if you had said 12 months ago that Theresa May would be the next leader of the Conservative party, you would have got generous odds for a hunch that has now proved correct. May played a long political game well to become prime minister. She may be embarked on a second over Brexit. The future of a nation and its people is at stake.