Boris Johnson stands triumphant, having successfully edited Theresa May’s Brexit deal. Not for the first time, a man has claimed the credit for a woman’s work. But has Johnson really solved the Brexit conundrum, or is this yet another tissue of lies? Will his proposals stand up to scrutiny if parliament convenes at the weekend?

Here’s why Johnson’s plans have every chance of falling apart. The first weak point is still Northern Ireland. The plan for maintaining a stable alignment of regulations between the Irish Republic and Northern Ireland might seem reasonable: Stormont is set to get a vote every four years, with a two-year cooling-off period. But looking into the future, this quickly collapses. What happens when the rest of the UK decides to follow a different regulatory path, as promised by this hard-right Conservative government? If there can be no land border, there would have to be regulatory checks in the Irish Sea to maintain the integrity of the single market. Moving the regulatory border to the Irish Sea would be a significant and practical step towards reunification. It therefore makes sense that the DUP will not back it. The political limits of “one country, two systems” are obvious.

Britain cannot be Sweden and Singapore at the same time. It can’t be in the US and EU regulatory sphere simultaneously

But the real mistake is to analyse this deal on its own terms, rather than those of the national interest. Important as it is to question whether it is coherent and durable, that also misses the point. Johnson’s deal is predicated on the fiction that Britain has more to gain from new trade deals with faraway countries than from maintaining frictionless trade with our nearest neighbours, which already account for half our trade, as part of the world’s most powerful trading bloc. The government’s own figures show that a hard Brexit – outside the customs union and single market – will leave every household more than £2,000 poorer.

In truth, Brexit is best understood as a prism through which an argument about the future of the country has been refracted. That’s why the argument over the level playing-field provisions in the political declaration is so important. For the ERG, the strategic purpose of Brexit has always been to deregulate at home in order to strike trade deals with the US and emerging markets, since most modern trade deals are less about tariffs and more about regulation, and their political goal is to realign Britain from the EU to the US.

Meanwhile, wavering Labour MPs have sought assurances on high standards, workers’ rights and environmental protections – which are all essential to keeping Britain a social democracy with a mixed economy. But both versions of the future cannot be true. This isn’t a matter of opinion but logic. Britain cannot be Sweden and Singapore at the same time. It can’t be in the US regulatory sphere and the EU sphere simultaneously.

So how has Johnson done this? The key is the different status of the withdrawal agreement and political declaration. While the political declaration will enter domestic law, it is only a statement of intent, and lacks the enduring status of an international treaty commitment. Johnson can therefore promise the ERG that after winning a majority in a general election, he will set aside the political declaration and pivot towards deregulation and a sweetheart trade deal with Donald Trump. The ERG have plainly been led to believe that Johnson’s deal will allow their version of the future to flourish, or they would not be supporting it.

Labour MPs will have to think very carefully and ask themselves if Johnson is lying to them and the British people, or if he is instead lying to the ERG. Those who vote for his deal will not just have to believe what he has said – they will have to trust his future intentions and ability to deliver on them. If Johnson succeeds and proceeds to sell-off the NHS to Donald Trump while slashing workers’ rights and environmental protections then history will put any Labour MPs who allowed it to happen in the top tier of the useful idiots of our era. And all to deliver a deal that weakens our economy, diminishes our influence and divides our country. It is an awfully large gamble to take on a man whose rise to power has revealed a void where moral character should belong.

• Tom Kibasi is a writer and researcher on politics and economics