Last week I wrote a speech for Theresa May, which concluded with an announcement that she had decided Brexit was impossible to deliver. Sadly she didn’t listen, and so onwards she leads us towards the cliff edge. I am hoping for better luck with Jeremy Corbyn, fantasising that he delivers this speech to a rally of his faithful Momentum followers …

“Thank you for that wonderful reception. Yes, yes, I know my name. ‘Oh Jeremy Corbyn’. Yes, that’s me. Now please stop singing and sit down. Please.

“I will be honest with you. I didn’t want the job. I didn’t think I would get the job. I wasn’t sure I could do the job. But thanks to you I got it. Thanks to you I now have the confidence to do it. I approach the challenge of being prime minister not with fear or trepidation but with confidence that our time is coming. That it is our duty now to serve. Protest is one thing. Government is another. And we must now prepare, genuinely prepare, as a government in waiting.

“If I become prime minister it is Brexit that will define my leadership. As a result of what happened on 23 June 2016 I have no choice in the matter. The people’s choice dictates that it is so.

I have concluded that rejecting this vision of Brexit is the only route to the vision of the world that drives us

“It is clear to me the constructive ambiguity of our position on Brexit is no longer tenable. It is fine for a party of protest. It is not good enough for a party one step away from government.

“Let’s imagine this entirely credible scenario. As the current chaos inside the government continues, Mrs May falls. The Tories try to foist another prime minister on us, chosen by their ageing membership. But we and the public won’t wear it. We force an election. We win an election. I am prime minister. Now the hard part begins.

“What does our ‘jobs-first’ Brexit mean then, in power? What is a jobs-first Brexit if our leaving the single market hurts growth, as every analysis in the world says it will? What is a jobs-first Brexit dependent on trade if trade slows and even grinds to a halt with the absence of a proper customs infrastructure at our ports, the absence of good trade deals not just with the EU but with the 66 countries with whom we have deals as part of the EU? What is a jobs-first Brexit if firms decide that if the UK leaves the EU, they leave the UK, and take their jobs and their tax take with them?

“And how can we fund all the things in our election manifesto that we need and want to fund in the future if our economy tanks?

“At Labour’s party conference, I said that our continued membership of the EU would prevent us from implementing many of the plans in our manifesto. I am grateful to the New European, which sought legal advice in Brussels and established this was not the case. So the question becomes, not ‘What do we lose by staying in?’, but ‘What do we lose by coming out?’

“The dominance of the hard right is clear in their pressing Mrs May to walk away from the negotiations, crash out of the EU, into the World Trade Organisation. I am of the internationalist left. We exist to fight the nationalist right, not to dance to its tune. We believe in support for the many, not the prosperity of the few. It is the nationalist right that is leading the Brexit Mrs May is pursuing, whatever the cost. It is their only route to the vision of the world that drives them. And, today I want to tell you – I have concluded that rejecting this vision of Brexit is the only route to the vision of the world that drives us. In this debate, they are the reactionaries, we and the Europeans the progressives.

“Take back control, they said. But what kind of control? Their control. Their right to dump decades of law with their ‘great repeal bill’, and bring about their vision of a low-tax, low-regulation economy, public services there for profit not public, employment and environmental rights shredded, one of the great powers of the world reduced to a gigantic Cayman Islands. That is their dream. And many of those who voted for Brexit, in the poorest areas, the places we represent, they will be the hardest hit. As the reality of power nears, I must tell you, candidly, that I can no longer go along with it. Not now. Not in two years. Not ever.

The time has come for Theresa May to tell the nation: Brexit can’t be done | Alastair Campbell Read more

“No deal, I must warn you, would be a catastrophe. So if Mrs May is still prime minister, and presents the no-deal option to parliament, be in no doubt – we will vote against it. We will press for a deal that keeps us in the single market and the customs union, to protect trade and avoid chaos.

“But today I want to go further. The referendum was close. It was not, contrary to the claims of the Brextremists, ‘clear’, let alone ‘overwhelming’. Millions are deeply concerned about what is happening to our country. I believe people have a right to change their minds as this all unfolds. And politicians have a duty to reflect that, and to give proper vent to the debate it represents.

“Democracy is a process, not a moment in time. If the government falls, and we win an election, then we can put a different vision of Brexit to the country, and we will. If we can bring about a fresh election, this is the Brexit policy you will be voting for.

“We will take over the negotiations from Mrs May and her hapless, hopeless team. We will review what progress has been made and assess whether Brexit can be delivered on the timescale set out under the article 50 process she triggered.

“If we conclude, as on any current assessment seems likely, that Brexit cannot be delivered without real damage to our economy, that a jobs-first Brexit is impossible, that it will mean lower growth, higher prices, higher unemployment, more austerity, cuts to public services, customs chaos, the return of a hard border in Ireland and the potential undoing of the Good Friday agreement, the loss of security cooperation with our partners, then I will revoke article 50.

“I am clear that a referendum decision can only be overturned by another one, and so we will legislate for a new referendum, and the choice we will put before the British people is between staying in, or leaving on the terms then on offer.

“If, as I believe they will, the British people opt to reverse their decision of last June, that will put us in a strong position then to succeed where David Cameron failed, and win the argument for a reformed EU that works for all.

“Comrades, this has been a lot to take in. But I believe it is the right course for our party, for our movement, and most important of all, for the country.

“This is our country too. This is our time. Let’s take back control of our destiny, and build a country future generations will be proud to call home. Thank you.”

• This is an edited extract from a piece in the New European

• Alastair Campbell was Tony Blair’s director of communications and is editor-at-large of the New European