In the progressive half of British politics we need a plan to put our stamp on the Brexit result – and fast.

We must prevent the Conservative right using the Brexit negotiations to reshape Britain into a rule-free space for corporations; we need to take control of the process whereby the rights of the citizen are redefined against those of a newly sovereign state.

Above all we need to provide certainty and solidarity to the millions of EU migrants who feel like the Brits threw them under a bus this week.

In short, we can and must fight to place social justice and democracy at the heart of the Brexit negotiations. I call this ProgrExit – progressive exit. It can be done, but only if all the progressive parties of Britain set aside some of what divides them and unite around a common objective.

The position of Labour is pivotal. Only Labour can provide the framework of a government that could stop Boris Johnson, abetted by Nigel Farage, turning Britain into a Thatcherite free-market wasteland.

Labour – and I mean here the 400,000 people with party cards and a meeting to go to – must go beyond the analysis and grieving stage, and do something new.

First, Labour must clearly accept Brexit. There can be no second referendum, no legal sabotage effort. Labour has to become a party designed to deliver social justice outside the EU. It should, for the foreseeable future, abandon the objective of a return to EU membership. We are out, and must make the best of it.

Next, we should fight for an early election. Almost all parts of the Labour movement have reason to resist this: for the Blairites it holds the danger that Corbyn will become PM – something they thought they had years to sabotage. For Corbyn, the nightmare is he gets stuck as a Labour prime minister with a Parliamentary Labour Party that does not support him. For the unions, they are out of cash. For the new breed of post-2015 activists, bruised by being told to eff off by what they assumed were their core supporters, it feels like a bad time to go back on the doorstep. But we must go there.

An early election – I favour late November – is the only democratic outcome in the present situation. No politician has a mandate to design a specific Brexit negotiation stance now. The only one with a democratic mandate to rule Britain just resigned, and his party’s 2015 manifesto is junk.

Europe cannot conduct meaningful Brexit negotiations with a scratch-together rump Tory government. So the whole process will be on hold.

In the election Labour should offer an informal electoral pact to the Scottish National Party, Greens and Plaid Cymru. The aims should be a) defeating Ukip and b) preventing the formation of a Tory-Ukip-DUP government that would enact the ultra-right Brexit scenario.

Caroline Lucas has indicated the price of such a pact might be a commitment to proportional representation. Labour – which cannot govern what is left of the UK alone, once Scotland leaves – should accede to this.

If, as a result of the snap election, Labour can form a coalition government with the SNP, Plaid and Greens, it should do so.

However, the most obvious problem is the position of Scotland. Nicola Sturgeon is right to demand a new independence vote, and to explore how to time that vote in a way that maintains Scotland’s continuous membership of the EU.

Given the strength of the remain vote in Scotland, Scottish Labour is faced with a big decision: does it oppose independence and go with Brexit to maintain the Union, or switch now to promoting independence to stay in the EU? I favour the latter, but it should be for Scottish Labour members to make that decision independently.

At Westminster, however, Labour should offer – in return for a coalition government – a no-penalty Scottish secession plan from the UK, funded and overseen by the Treasury and Bank of England.

Proportional representation, coalition government and Scottish independence were not in Labour’s game plan at 10pm on Thursday night. But neither was Brexit.

If the political ideas in your head, cultivated over a lifetime, rebel against all this, you must get used to it: with or without the help of the PLP, Scotland is headed out of the UK. But Labour has the opportunity to make that separation amicable; it will be obligatory for all progressive parties to ally with the Scots as – inevitably – the authoritarians of Ukip try to prevent Sturgeon’s second referendum.

As to what a Labour/SNP/Plaid and Green coalition would argue in the Brexit negotiations, the baseline has to be maintaining the existing progressive legislation on employment, consumer rights, women’s rights, the environment etc. But at the same time a Labour-led Brexit negotiation would have to drive a hard bargain over ending bans on state aid, or on nationalisation.

If it were possible to conclude a deal within the European Economic Area I would favour that. But the baseline has to be a new policy on migration designed for the moment free movement ceases to apply. It should be humane, generous, and led by the needs of employers, local communities and universities – and being an EU member should get you a lot of points.

But – and this is the final mindset shift we in Labour must make – free movement is over. Free movement was a core principle of the EU, developed over time. We are no longer part of that, and to reconnect with our voting base – I don’t mean the racists but the thousands of ordinary Labour voters, including black and Asian people – we have to design a migration policy that works for them, and not for rip-off construction bosses or slavedrivers on the farms of East Anglia.

Britain is not, as the far left peevishly dubbed it, “rainy, fascist island”: we’ve snatched glory from the jaws of ignominy in our history before now – but only when politicians have shown vision.

If they don’t show vision, we – the rank and file of Labour, the left nationalists and the Greens – who have way more in common than political labels suggest, should force them to unite and fight.