Politicians are prisoners of the choices they make. The humiliation of the Prime Minister in Brussels yesterday, forced in front of the world to turn around and go home because she did not have the authority to sign a deal on behalf of her country, was not the fault of the EU, or caused by the intransigence of the Irish, or because the DUP were unreasonable.

It was a direct consequence of decisions made by Mrs May and her government last year.

The British people were asked only one question in the referendum: “should the UK remain a member of the EU or leave the EU?”

It was Mrs May’s government that chose to interpret the result as a decision to leave not only the European Union but the single market and the customs union too. They are not synonymous.

Norway is in the single market, and Turkey is in the customs union, but neither are members of the European Union.

Of course, there is a price to be paid if you are part of the single market or customs union but not in the EU. You have less influence over regulations that affect your country and its businesses.

Yet the likes of Norway and Turkey, and Switzerland through bilateral agreement, are proud of their sovereignty but believe it is a price worth paying for the frictionless access you get to the European market.

Our Government, with no detailed analysis, or any careful weighing of the options, simply asserted that it was not a price worth paying.

It told us being outside the single market gave us the chance to cut red tape, and that leaving the customs union meant we could strike trade deals with the rest of the world.

Never mind that every idea from the Government since the vote has been for more red tape, and no trade deal being suggested — even if passed — can make good the loss of trade with Europe.

Border

What the Government didn’t tell us was that this approach inevitably meant a hard border with the Irish Republic, because the two countries on either side of it would have different regulations.

Ireland, which now has a veto over Britain’s future thanks to Brexit, said “no”. To square the circle, Downing Street came up with what Baldrick might call a “cunning plan” whereby Northern Ireland would have “regulatory alignment” with the south and the EU — even if the rest of the UK would not.

Decisions affecting Belfast would be taken in Dublin and Brussels, not London. Over time this would (as Denis Staunton of the Irish Times writes opposite) lead to an all-island economy, and make “a United Ireland more likely”.

The irony that the Brexiteers might be doing more to advance the cause of Irish nationalism than O’Connell, Parnell and Gerry Adams was not lost on the DUP. So Ulster said “no”.

You might have thought the PM would have checked with the faction that is keeping her in power before offering her plan to the EU. Clearly not; hence the fiasco yesterday. So what next?

Today Scottish Conservative leader Ruth Davidson, who commands far more authority among Tories than Mrs May, pointed out the obvious. We have to keep the Irish border open. That means keeping the rules that apply on each side of it broadly the same.

But we can’t countenance, in her words, a Northern Ireland-only deal which “compromises the political, economic or constitutional integrity of the UK”.

So logic suggests that “regulatory alignment” with the EU “must be on a UK-wide basis”.

In short, although Mrs Davidson won’t say so, Britain should stay in the customs union and perhaps the single market.

Whether it’s a formal arrangement, or a hybrid one like Switzerland, we’ll see.

Labour has come to the same conclusion. And, as the Evening Standard noted the day after the general election, the lost majority means Mrs May doesn’t have the votes to resist.

So we’ll leave the EU but largely abide by EU rules that we no longer help write.

Once again, Ireland has taught us some home truths about the decisions our politicians make.