Oppositions that complain when the government calls an election are on shaky ground. In general, voters like the idea that a party that lost the last election wants to win the next one as soon as possible.

But when an election is called outside the normal electoral cycle by a government with a majority, the reason for calling that election deserves scrutiny and justification. On Tuesday, speaking outside No 10, Theresa May said the reason lay in divisions within parliament. “The country is coming together but Westminster is not.” She then set out the details of how opposition parties have been doing the job of opposing her since she became prime minister. This constitutional function she referred to as “political game-playing”, robbing Britain of “stability and certainty”.

It’s difficult to know where to start with this public rationale for an early election. But let’s begin with bald-faced hypocrisy. For months, May has been repeatedly and publicly denying that she will call an early election. Her justification has consistently been that it would add uncertainty and instability at a dangerous time for our country. It is one thing to U-turn by setting aside that argument, but quite another to cite the same reasons of stability and certainty as recommending precisely the opposite course of action a few days later.

And then there’s the annoying issue of the facts. Such is the constitutional might of the forces of evil arraigned against May’s government that 77 days ago she won a decisive vote in the House of Commons to trigger article 50 by 498 votes to 114. A majority of 384. The truth is that her majority Conservative government has not faced a single irreversible setback from Westminster relating to Brexit.

This election is nothing to do with overcoming unconstitutional parliamentary obstacles to Brexit. But it is about power, and it is about our constitution. To understand the early election, you only need to understand the three enemies that May has in her sights.

The first enemy is the Labour party. Let’s be honest: she smells blood. Labour is not in a good way: divided over next steps on Brexit, over our leadership, and suffering a British version of the philosophical malaise that plagues all centre-left parties since the 2007-8 financial crash. She wants to destroy Labour for a generation. Nothing wrong with that if you are a Tory, of course, but let’s not pretend the temptations of political opportunism are tinged with the nobility of the national interest.

The second enemy is her own party’s soft-Brexit rebels. The PM wants an election to rid her of the turbulent sceptics in her own party who both threaten the Brexit deal and ask awkward questions about it as it emerges, and express doubts about domestic policies that depart from the 2015 Tory manifesto (on grammar schools, industrial policy, national insurance contribution increases, dropping the 0.7% aid target). May could have been honest about this. She could have said in Downing Street that she wanted her own mandate for her own government. That would have been a courageous and unarguable rationale. But she didn’t.

But the third enemy is the most concerning of all: parliament. The prime minister has called an election to enable her to more effectively circumvent parliamentary scrutiny of Brexit. In the coming years we already face the prospect of a so-called great repeal bill – an unprecedented wholesale transfer of thousands of EU provisions into UK law by departmental fiat rather than through the normal legislative process. That in itself is an affront to a country with the cardinal constitutional principle of parliamentary sovereignty.

But after 9 June, things could get a whole lot worse. A May government would see the election result as a blank cheque for its yet-to-be-defined version of hard Brexit. In the coming years, our government will be conducting Brexit negotiations that involve the most crucial, complex and far-reaching set of issues imaginable.

What she is seeking in the election is a majority that can be presented, day after day, as a justification for branding those in parliament who scrutinise, question or query – let alone challenge or oppose – these details as “enemies of the people”.

That is what this election is about. And Labour needs to realise it. We may want the decision facing the country to be about alternative economic visions or contesting views of public services. They are crucial issues, but they won’t be the focus of this election. This is a Brexit election. Not a rerun of the referendum, but an election about what kind of parliament we want at the most important national moment in Britain’s history since 1945.

The case for Labour at this historical moment must be to protect our country not against the fact of Brexit, but the version of hard Brexit that May wants to pursue unencumbered by scrutiny. A Brexit that tosses our membership of the single market aside, making way for a low-wage, low-tax, low-regulation future that marries a vision of offshore Britain with dependence on foreign capital from wealthy authoritarian regimes around the world. A Brexit that will damage not just the poorest and most vulnerable among us, but British business and the union itself.

Labour might not have wanted an election now, nor a Brexit election at all. But that’s what we have, and we would be betraying Britain to pretend otherwise.