Theresa May can never be trusted on anything she says ever again. She is a patently dishonest politician who cannot keep her word, because for her, partisan self-interest is more important. Her position was clear. A few weeks ago, May’s spokesperson said: “There isn’t going to be one. It isn’t going to happen. There is not going to be a general election.”

May claims that her U-turn on a snap general election was driven by the threat of Brexit being obstructed by parliament. This is a lie. There is no obstruction. To the chagrin of many ardent remainers, Labour voted through article 50 and emphasised it would respect the will of the British people.

General election 2017: Theresa May says opposition to Brexit plan behind decision - Politics live Read more

May was the remainer who reinvented herself as a hard Brexiteer, again for partisan self-interest. May was the leader who allowed her chancellor to break a key Tory election pledge on national insurance, only to U-turn when the betrayal became impossible to argue for because of her small majority.

She said that now wasn’t the time for a Scottish independence referendum because of the instability it would cause, and then plumps for an unnecessary general election. She announced a pause on the Hinkley Point C nuclear power station and then – under pressure from China’s regime – U-turned.

Play Video 1:04 May's election U-turn: the times she ruled out a snap vote - video

You Can’t Trust May is just one possible approach for Labour as election-weary voters ask why they have been asked to yet again march to polling stations. But, look. Labour’s current polling is very, very bad indeed: you can’t try to climb a mountain if you are deluded about how high it is. The threat of an early election these past few months should have haunted every moment, for Labour’s left and its trade union allies: those of us who wanted a Labour party that was firmly rooted on the left on the economy, tax and public services, and which could inspire enough people to vote for it.

A man who stood only out of a sense of duty, to put policies on the agenda, and who certainly had no ambition to be leader, will now take Labour into a general election, against all his original expectations. My suggestion that Corbyn stand down in favour of another candidate was driven by a desire to save his policies – which, as the polling shows, are very popular indeed – from being buried in the rubble of a terrible election defeat. They made the decision last June and since – yes, in accordance with the majority of Corbyn’s supporters – not to do so. So now what we must do is unite and do our very best to prevent a Tory landslide that would be calamitous for the country.

This referendum is about Brexit above all else. Labour has understandably agonised over losing the minority of its voters who plumped for leave, not least in its northern heartlands and among older voters who are more motivated to turn out to cast their ballots. It must now make a pitch, too, for despondent remainers.

Yes, that means reassuring leave voters that they will respect the referendum result. But the party must pitch for the 48% who voted remain. May has nothing but contempt for them. They are being not just ignored, but demonised. They are being denied a say over the future of our country. Only Labour can represent you, and the party will do so with every fibre of its being.

Play Video 1:01 'I welcome the opportunity': Jeremy Corbyn on 8 June general election

Labour will stay in the single market and the customs union. That must be the argument. The party must say: we will defend the rights and benefits that we currently have, which benefit the majority of the country. That will be the basis of any Brexit deal. If the Tories win an immense majority, a ruinous hard Brexit could beckon. If you want to put jobs, the economy and living standards first, you must vote Labour to stop a landslide victory that could turn Britain into a barren tax haven run in the interests of billionaires. Wages are starting to fall: no doubt just one reason why this election was called. Rather than going back to diagnosing a “cost of living crisis”, Labour must set out how it will cure it.

May has called a snap general election. Our writers respond | Zoe Williams, Matthew d’Ancona, Martin Kettle, Sonia Sodha, Simon Jenkins, Ruth Wishart, Gaby Hinsliff Read more

Some will be tempted to vote for the Lib Dems again. Their years of propping up a Tory government – which has led Britain to this calamitous moment – must be emphasised. Tim Farron is on record committing his party once again to a coalition with the Conservatives. He even sided with Donald Trump as soon as he started firing missiles. There is no party so demonstrably dishonest in modern British political history. In any case, our electoral system means that Lib Dem chances of winning a considerable number of seats to champion the remain cause are minimal.

As has been noted, Labour’s recent policies are indeed electorally very popular. You don’t win elections, though, with policies that – taken individually – have high levels of support, as Ed Miliband discovered. There has to be a vision to bring them together. If you don’t define what you are for, you will be defined by your opponents, already the critical problem afflicting Labour’s leadership. You need a sunny, optimistic vision, not a miserable shaking of the stick at everything that’s wrong.

Investing in the Future, for example. Labour privately briefs that the theme of its recent policies is standing up for the 99% and standing up to the 1%. That has to be conveyed in a short, snappy phrase – like Long Term Economic Plan did for the Tories. Above all else: find a vision and stick to it, relentlessly. Every policy you announce must then slip into that frame: so rather than being another good idea thrown into the ether, it emphasises to the electorate what you are about.

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And here’s a message for Labour’s immense grassroots army. This is your moment. No excuses: every single one must take to the streets, knocking on doors every possible night that you can, getting the message across, ensuring that on election day there’s the biggest get out the vote operation in the history of British democracy. That may make a sizeable difference in terms of how many seats are won or lost. Voting in a leadership election was not enough, or even close. Go out and fight with everything you have.

There is no point being dishonest here. The Tories have called this election for naked partisan interest: it is cynical and dishonest, but from their own perspective, the logic is self-evident. Everything will now be thrown at Labour and its leadership: and the party starts from a very low base indeed. Corbyn decided to stay, and – with the national platform he will now have – he and his team must prove they can put forward an inspiring and coherent vision. Expose a dishonest Theresa; fight for a Brexit deal that puts jobs, the economy and living standards first; and stand for a Britain run in the interests of the majority, not the elites. Save the postmortem for whatever happens. Now it’s the time to fight.