The campaign against Brexit has been one of the most unsuccessful political movements in the world. It all started when David Cameron had a bright idea. “I thought it right to hold the referendum because this issue had been poisoning British politics for years,” he said recently. The referendum would get rid of the irritation that had been yapping at his ankles ever since he became Conservative leader.

Indeed, he became leader by shrewdly appeasing the Eurosceptics in his party. He promised to pull out of the European People’s Party – Angela Merkel’s outfit – in the European Parliament. In return, he expected the Tories to stop “banging on about Europe”.

They didn’t. They demanded a referendum on the Lisbon Treaty, which was what the EU Constitution became after it was defeated in referendums in France and the Netherlands. When the treaty was ratified by the British Parliament in 2008, Cameron dropped his demand for a referendum on it because it was too late. And his party did stop “banging on” for a bit, because there was an election on.

But then, after he became Prime Minister, they started up again: huge backbench rebellions on demands for a referendum; the rise of Ukip. So he decided, in 2012, to drain the poison by promising a national vote on Brexit, a term first used by Peter Wilding in a blog in May that year.

Theresa May grimaces after being told she admitted Brexit was to blame for people's problems

Ed Miliband resisted the pressure from Ed Balls, his shadow Chancellor, to match the promise of an EU referendum and so the 2015 election became, in part, a choice between affirming Britain’s membership of the EU and taking a risk with it. We know how that worked out.

The campaign against Brexit then mobilised everyone from Barack Obama to the Pope to argue for staying in, and we know how that worked out too.

​Remainers sometimes say that the result was close, which it was. There was just 1.8 per cent in it, which meant that if one Leave voter in 50 had voted Remain it would have gone the other way. On the other hand, when you consider that not just Obama and the Pope but the Prime Minister, the Leader of the Opposition, three-quarters of all MPs, the Governor of the Bank of England, the CBI, TUC and JK Rowling all said leaving the EU was a bad idea, the 52 per cent Leave vote was pretty emphatic.

After the referendum, the rearguard action to try to reverse it, reconsider it or at the least to keep options open about it turned out to be just as counter-productive. An expensive court case to force new Prime Minister Theresa May to put the invoking of Article 50, the formal process of leaving, to votes in Parliament was successful. Both Houses of Parliament then voted by large majorities to do so. In the Commons the vote was 80 per cent. In the Lords it was 70 per cent.

In pictures: European parliament Brexit discussions Show all 12 1 /12 In pictures: European parliament Brexit discussions In pictures: European parliament Brexit discussions European commission member in charge of Brexit negotiations with Britain, French Michel Barnier listens at the President of the European Commission Jean-Claude Juncker speaking at the European Parliament in Strasbourg Getty Images In pictures: European parliament Brexit discussions Frank-Walter Steinmeier, President of the Federal Republic of Germany, delivers his speech at the European Parliament in Strasbourg EPA In pictures: European parliament Brexit discussions European Union's chief Brexit negotiator Guy Verhofstadt, President of the Group of the Alliance of Liberals and Democrats for Europe (ALDE), addresses the European Parliament during a debate on Brexit priorities and the upcomming talks on the UK's withdrawal from the EU Reuters In pictures: European parliament Brexit discussions Michel Barnier, European Chief Negotiator for Brexit reacts during a meeting at the European Parliament in Strasbourg EPA In pictures: European parliament Brexit discussions Member of the European Parliament and former leader of the anti-EU UK Independence Party (UKIP) Nigel Farage wears socks with Union Jack flag at the European Parliament in Strasbourg Getty Images In pictures: European parliament Brexit discussions Nigel Farage, United Kingdom Independence Party (UKIP) member and MEP, addresses the European Parliament during a debate on Brexit priorities and the upcoming talks on the UK's withdrawal from the EU Reuters In pictures: European parliament Brexit discussions European commission member in charge of Brexit negotiations with Britain, French Michel Barnier gestures during speeches at the European Parliament in Strasbourg Getty In pictures: European parliament Brexit discussions The President of the European Commission Jean-Claude Juncker (L) speaks with European commission member in charge of Brexit negotiations with Britain, French Michel Barnier at the European Parliament in Strasbourg Getty In pictures: European parliament Brexit discussions European Union's chief Brexit negotiator Guy Verhofstadt, President of the Group of the Alliance of Liberals and Democrats for Europe (ALDE), addresses the European Parliament during a debate on Brexit priorities and the upcomming talks on the UK's withdrawal from the EU Reuters In pictures: European parliament Brexit discussions Member of the European Parliament and former leader of the anti-EU UK Independence Party (UKIP) Nigel Farage gestures during speeches at the European Parliament in Strasbourg, eastern France, on April 5, 2017. The European Parliament will on April 5 lay down its "red lines" for negotiations over a Brexit deal, on which the assembly will have the final say in two years' time. / AFP PHOTO / Sebastien BozonSEBASTIEN BOZON/AFP/Getty Images Getty In pictures: European parliament Brexit discussions German president Frank-Walter Steinmeier delivers a speech during a plenary session at the European Parliament in Strasbourg Getty In pictures: European parliament Brexit discussions The European Parliament in Strasbourg, eastern France Getty Images

Any doubts about the legitimacy of the referendum should have been quashed by those votes. If the referendum were merely “advisory”, as some of the rearguard pointed out, then Parliament had considered that advice and acted on it.

Yet the campaign against Brexit continued. Tony Blair found an audience for his analogy about agreeing a house swap without seeing the other house and reserving the right to a change of mind on viewing – or, in this case, after the terms of Brexit had been negotiated. Tim Farron demanded a second referendum, although that would require the EU 27 to accept that Article 50 was reversible, and it would guarantee that they would offer us nothing in the Brexit negotiations, in order to try to change our minds.

But it was Keir Starmer, the shadow Brexit Secretary, and Jeremy Corbyn who took the next counter-productive step. They refused to say that Labour MPs would vote – in the final vote that May had promised Parliament – to endorse whatever Brexit deal she came back with. Naturally enough, they did not want to support in advance a “no deal” outcome of the Brexit talks.

That apparently sensible bit of constructive opposition blew up in their faces when May stepped out of No 10 to announce, at the uncrested lectern, that she was calling an election because “in recent weeks Labour has threatened to vote against the deal we reach with the EU”. No doubt she would have found another reason to go to the country if Labour hadn’t given her that opening, but it is remarkable how every attempt to keep open the option of a second thought about Brexit has resulted in its being more firmly closed.

We expected what followed to be the Brexit election, devoted mostly to the question, Who do you trust to negotiate our departure from the EU? It hasn’t turned out like that, although it is likely to return to that question in the final 11 days. But it remains true that this election is, in effect, a second referendum on the Brexit question. Those who don’t accept the result of the referendum, despite the Article 50 votes in Parliament, will have lost their last line of defence if Theresa May wins a parliamentary majority on an explicit manifesto promise to leave the EU.

And, if she wins, she will have a free hand (with the possible exception of the undemocratic House of Lords) to negotiate Brexit as she sees fit.