THERESA May and Nicola Sturgeon may have been smiling in the official pictures of their meeting in Glasgow, but any attempt at cordiality could not hide what is really going on between the Prime Minister and the First Minister. Relations are strained; the two governments are in opposite trenches; and the prospect of consensus on Brexit is now dead.

This was not the way we were told it was going to be. Shortly after taking office last year, Mrs May talked about trying to achieve a collaborative deal on Brexit; the devolved governments would be consulted, she said; and the UK Government would consider the views of the Scottish Government on a special deal for Scotland.

But where is the idea of collaboration now? Speaking ahead of her talks with Ms Sturgeon, the PM said she wanted to ensure the best possible deal for the whole of the UK on Brexit, including Scotland, but there were no concessions on Ms Sturgeon’s demands for a distinctive deal or any guarantees on the repatriation of powers from the EU. It has done little to dispel the impression of a UK Government that is listening in principle but working to its own agenda in practice.

As for the timing of a referendum on independence, it looks very much like the wind is blowing in Ms Sturgeon’s direction. According to the SNP’s take on the meeting, the PM said she expects an agreement on Brexit and future trading relationships with the EU to be finalised in 18 to 24 months. Of course, there is every prospect that is way too optimistic, but if that is Mrs May’s expectation, it makes it much harder for the UK Government to achieve what it would really like to do, which is delay a referendum until after the 2021 Scottish elections.

Whatever happens, the final date for a referendum will still have to be guided by the Brexit negotiations – voters must know clearly where they stand before any vote takes place. Then there is the question of the official procedure for setting the question and deciding other matters; there also needs to be a decent time for a proper campaign – a referendum cannot be held the day after the end of the Brexit talks.

However, now that the Prime Minister has conceded the principle of a referendum, she cannot go on delaying forever. Indeed, parts of her speech in East Kilbride sounded like the campaign had already started. “When this great union of nations sets its mind to something and works together with determination,” she said, “we are an unstoppable force.”

Perhaps this is an indication the Unionist argument this time around will attempt to move away from accusations of “Project Fear”. But the problem for Mrs May is that she is arguing for protecting one union while negotiating to leave another. She talks about working together within the UK, but in pursuing a hard Brexit, appears willing to ignore the damage it will do – indeed, is already doing – to the British economy.

She also appears willing to risk the potentially serious consequences for the future of the UK and call Ms Sturgeon’s bluff, and we all know what happened with that: today, the Scottish Parliament will likely back another referendum on independence.