WE'RE all familiar with the game of chicken from Hollywood films. Two testosterone-fuelled men drive head-on at high speed in the sure knowledge that the weaker will eventually swerve to avoid catastrophe – only sometimes they don't. But it seems women are just as capable of playing this dangerous game.

Theresa May and Nicola Sturgeon are currently accelerating towards a crash of constitutional authority which could annihilate one or both of them. Neither is giving in. The Prime Minister is no longer promising any specific new powers for Holyrood, let alone continued membership of the EU single market. The First Minister is insisting that if May doesn’t deliver she'll call a second independence referendum. Something has to give.

Back in 2012, Alex Salmond and David Cameron, for all their dangerous driving, ended up with the Edinburgh Agreement. But times change. The UK is a different place now, and compromise and concession are out of date. Look how the UK Government is refusing to give EU citizens living and working in the UK for decades any assurance that they won't be deported post-Brexit.

No British government in the last century has behaved this way, outside wartime. Holding the welfare of three-million EU nationals hostage to Brexit negotiations is simply uncivilised. The moral responsibility is clearly on the UK to behave reasonably to those who came and lived in the UK in good faith. But good faith is old hat in the brave new world of Brexit.

Before the June referendum, prominent Leave spokesmen like Michael Gove and Tom Harris were promising all manner of extra powers for the Scottish Parliament after Brexit. The former Tory Lord Chancellor said Holyrood could gain powers over immigration. Harris said Holyrood would get a £1.5 billion cash windfall, plus savings from no longer paying the fees of EU students. Both suggested that Scotland would automatically get new powers on devolved areas like agriculture, fisheries, environment, justice, even VAT.

Well, now we know. The idea that Holyrood would inherit the powers currently exercised by Brussels was always naive. As the Scottish Tory leader, Ruth Davidson, made clear last week, those powers will go “in the first instance” to Westminster and any that go to Holyrood thereafter will be the subject of “negotiation and mature discussion”. And she's not going to “give away her hand” in advance by specifying any. Holyrood's powers are now, like EU citizens, being held hostage to the creation of the new UK single market.

There will almost certainly be some new responsibilities in soft areas like justice and the environment. But the UK Government was never going to allow Holyrood to have its own Common Agricultural Policy, or decide the levels of Scottish agricultural support, currently £500m from Brussels. Nor was it going to allow the Scottish Parliament to have any say in trade negotiations with other countries, allow free movement, or set its own trading standards to remain EU compliant. Theresa May saw what happened when the Belgian region of Wallonia threw a spanner in the works of the Comprehensive Economic and Trade Agreement between the EU and Canada. Scotland won't be allowed to interfere or impede UK trade negotiations with America or the Commonwealth countries.

Holyrood complies with regulations set by Brussels on a whole range of issues: food standards, animal welfare, fishing quotas, genetically modified crops, product labelling, competition policy. In future, the Scottish Parliament will administer these regulations as it does now, but the overall policies will be set by Westminster, except in areas where the UK Government gives Holyrood specific concessions.

As Theresa May said at Prime Minister's Questions, nothing must be done to undermine the new “UK single market” after Brexit. In the EU single market, the European Court of Justice enforces standards across the entire EU to ensure free trade in goods, services, capital and labour. You can't sell meat in Europe unless it conforms to EU slaughterhouse regulations, or toasters unless they have the right safety features. Governments cannot gain unfair advantage by insisting on their own national rules, or “non-tariff barriers”. You can't discriminate against members of the EU coming to work or study. In future, when the UK single market replaces the EU, these standards will obviously be enforced centrally by Westminster to ensure UK-wide coherence.

This stands to reason. Some 85 per cent of Scottish agricultural exports go to England. If Scotland does not comply with UK regulations then they won't get sold there. Currently, Scotland cannot discriminate against EU students, and so they get free tuition. After Brexit, Scotland may find that under the UK single market rules it cannot discriminate against English students by making them pay fees.

Currently, the Scottish Government must allow private contractors to compete for contracts like CalMac ferry services or ScotRail. Nor can Scotland set minimum pricing of alcohol under EU competition law or subsidise the steel industry. In future, Westminster will set competition policy for the UK single market, including Scotland. Scots cannot set competition policy for the UK. There may be opt-outs and concessions on pricing rules, but that will be by negotiation, not as of right.

The misunderstanding about the transfer of EU laws arose because of the way the 1998 Scotland Act is drafted. Only the powers specified in Schedule Five are reserved to Westminster: the constitution, defence, financial and economic matters, immigration etc. All the rest are up for grabs, at least in theory. But what underpinned Scotland's law-making powers in the past was the overall jurisdiction of Brussels, to which all Holyrood statutes must conform. Theresa May made clear in her conference speech in Glasgow that this must change. The UK has to become much more closely united, she said. The days of “devolve and forget” are over.

The UK is engaged in the most comprehensive power play at least since 1998 as the UK becomes a centralised state again. Much of Scotland’s legislative autonomy will be extinguished as Westminster adds Brussels laws to those already reserved. No longer will it be assumed that the Scottish Parliament has power where Schedule Five is silent. In effect, we are now looking at Schedule Five plus – as the UK single market replaces the European one. Only those decision-making powers that the UK Government deems fit for devolution will go to Holyrood. And only if the Scottish Government pipes down and accepts its place in the New Brexit Britain.

For weeks, the Scottish Government has been expecting some kind of package of proposed Brexit powers to be offered by May in response to its proposal that Scotland should stay in the single market. Nothing has been forthcoming. Zilch. Theresa May is not prepared to play the old UK game of promising this or that in order to prevent Scotland holding a referendum. Making vows, promising new powers, accepting “no detriment” guarantees of continued funding.

This is a new United Kingdom in which Scotland must fit in or get out. Nicola Sturgeon says she “isn't bluffing” and that Scots will leave the UK, realising that the old devolution settlement is over. But the Prime Minister has been persuaded Sturgeon is not serious about independence, and even if she is, Yes2 will lose. Collision time is due in two weeks when Theresa May declares Article 50. And Nicola Sturgeon faces an SNP conference baying for a referendum.