A curious thing happened at the weekend. Our prime minister addressed a group of world leaders in Argentina and told them something which was demonstrably untrue. She said Brexit would be good for the global economy. No respectable economic forecast or application of logic substantiates the claim. Not a single person in the audience could have believed her. And barely anyone back home batted an eyelid.

This should have been a moment of searing national shame. A British prime minister astride the international stage parroted a nakedly false party propaganda line to the most powerful people in the world. She lied to their faces. And still nobody cared.

Perhaps after all this time Brexit has anaesthetised us to routine dishonesty. We accept that our leaders will promote fiction over fact. But Theresa May has a problem: falsehood remains Brexit’s only currency. The prime minister’s project is plunging into crisis not because the government is lying, but because for the first time it is having to tell the truth.

Since the publication of the deal and EU summit to sign it off, the tone of the debate has transformed. The government can no longer hide behind appeals for national self-belief. The withdrawal agreement provides 585 pages of printed reality against which to judge three years of worthless promises.

The first new sign of the times arrived in the skirmishes with Pedro Sánchez and Emmanuel Macron. The Spanish prime minister demanded written assurances that Gibraltar would not be included in the future trade deal without Spain’s consent. The government, which had always denied it might sell Gibraltar out in future negotiations, was forced to do just that. Almost immediately afterwards the French president warned that he could keep Britain in the customs union backstop if the UK withheld fishing rights. Concrete threats painfully exposed our empty bravado. Britain’s loss of leverage is no longer a Remain rumour. It is to be spelled out by international treaty.

In the days following the summit, the government’s delusions have met robust daily challenge. Its response has been to dig deeper into the bunker. It is as though the unclothed emperor has responded to his humiliation not by finally getting dressed but by ordering everyone else to get naked as well.

First, Theresa May stood in the Commons and repeatedly insisted that we would have the power to sign new trade deals. But the truth of the backstop is that the UK will be in a customs union with the EU indefinitely. We may want trade deals based on services but other countries want them for goods. If we cannot sell them what they want, they will leave our shop empty-handed.

May has of course spouted the trade falsehood for a long time. Now, however, there is a document which proves how wrong she is. MPs’ demands to see the government’s legal advice have produced today’s almost unprecedented contempt motion in the Commons. But even if ministers avoid punishment, Attorney General Geoffrey Cox appeared to stagger MPs yesterday with a basic legal fact: under the backstop the EU would curb our independent trade policy and determine our tariffs, without any formal UK input or end point. The government had either not understood that simple truth or rigorously attempted to conceal it. Now it is out.

Perhaps Brexit’s biggest lie was that it would make us more prosperous. The government’s new bout of truth-telling appeared last week in the form of its economic forecasts. They revealed that in the best possible Brexit scenario, economic growth would still contract. Even that modelling assumed trade deals which will almost certainly not happen and Chequers-style frictionless trade which the EU has already ruled out. The Bank of England similarly proffered that all options were economically inferior to remaining in the EU, and that the worst Brexit scenario would shrink GDP by 8 per cent.

Naturally, the government wanted these economic forecasts to drive home the dangers of leaving with no deal, and to scare MPs into voting for the disastrous agreement negotiated by May. But a movement which seeks to fossilise an electoral moment in June 2016 cannot eliminate the context. At no point did Vote Leave hint that Brexit would be even slightly inferior to remaining. On the contrary, the EU had supposedly stifled jobs and growth, and Brexit would unshackle us from its economic corpse. There would be a free-trade boom, increased household prosperity and a weekly £350m for the NHS. We would all get richer.

In a panic, the government now seeks to deploy the same revisionism peddled by Nigel Farage. People are not only interested in the economy, the Chancellor said. They also care about sovereignty and fishing, for example. And so we must call this out for what it is: a gaslighting of the British people. Polls from 2016 suggested that only a small minority of Leave voters believed that Brexit would make us poorer. The victorious campaign never conceded a fraction of lost economic growth. Effectively the Brexiteers must then assert that the public knew they were wrong but voted for them anyway. We voted to leave, as the new narrative goes, so either cannot have cared about the economy or actively wanted to lose money.

The public may be less susceptible to Orwellian communications tactics than the government hopes. Recent polls show a momentum towards Remain, with indications that up to 56 per cent of the population would now choose to stay. And today’s preliminary opinion by the Advocate General of the European Court of Justice kicks away yet a further government untruth: we can revoke Article 50, and likely do so unilaterally. Ministers are pinning their hopes on convincing voters and MPs alike that the alternative to its deal is the catastrophe of no-deal, but its tactics keep falling foul of documents and events. It cannot deliberately confuse people forever. Brexit is now collapsing not through dishonesty but reality.

Throughout this process May has deceived voters, colleagues, world leaders, and perhaps most importantly herself. Brexit, like her premiership, has literally depended on it. But she now fights her most important battle against objective truth and cannot win. The public is learning that, against its will, Brexit will deliver us less prosperity and less sovereignty. The prime minister will continue to scare people about the consequences of rejecting her dismal agreement, but MPs and voters know they have a right to a better future and the means to secure it. The government has cried wolf too many times—and now it is going to get eaten.