Caroline Lucas has today issued a striking public call for a new politics of unity among ‘progressives’ – among those, that is, who seek at minimum to rein in the excesses of neoliberal ‘business as usual’, Tory-style.

Caroline opens her article by praising Jeremy Corbyn, one of the Labour leadership contenders – and one whose view chime with the Greens on nuclear missiles, climate change and austerity. I second that praise. But let’s be honest. Corbyn’s chances of winning the leadership election are slim.

But many Labour voters, members, candidates and Parliamentarians – and by no means just those who support Corbyn – share much in common with Greens. And it’s crucial that all of us interested in implementing a genuine political alternative work together, whatever leader Labour elects.

Because the alternative is grim: it’s the risk that the awful moment when we saw the exit poll on the night of 7th May will be repeated again in 2020. And again, in 2025.

Constituency boundary changes in progress only make such outcomes all the more probable. The Telegraph told it straight when it reported senior Tories as saying: “Redrawing constituency boundaries to lock Labour out of power for a decades is at the top of the agenda for the new Conservative government.”

We desperately need electoral reform – but how to get it?

The 2015 General Election resulted in a radically distorted electoral map of Britain, and a majority Government lacking a solid democratic mandate, voted for by under a quarter of the electorate.

It’s now clear to anyone with a sense of justice that this country must abandon its antiquated electoral system and adopt a system of proportional representation. Especially promising is the ‘Additional Member System’ employed in the Greater London Assembly, which preserves the constituency link while ensuring overall proportionality of outcome.

The question that Caroline addresses in her Guardian piece is how we can make such electoral reform becomes a practical political possibility. For the next five years, we will be governed by the most reactionary beneficiaries of the current undemocratic system – and they won’t change it.

Like Caroline, I believe the time has come to consider a bold step. ‘Progressive’ parties need to discuss an informal electoral pact to avoid fragmenting the vote in winnable seats, if we are to elect a Parliament in 2020 that would have a progressive majority for democratic change.

Important testing-grounds are coming up: the London Mayoral election in 2016, for example, and the 2017 County Council elections – which are likely to result, if there are no pacts, in radically distorted ‘one-party-state’ outcomes. Both could serve as test runs for the 2020 general election.

Key to this is that the five ‘progressive parties’ should seek, regionally or nationally, to assist local parties to win ‘quid pro quos’ if some candidates are prepared to stand down for the greater good. If, for example, Green candidates are willing to stand down in Labour’s favour in some seats, then the compliment needs to be repaid, in a few others.

It won’t be plain sailing! But we must still try

The first criticism is that such a pact is unlikely to be able to be formed. Labour may cling, as it has in the past, to the idea of an all-out victory, the dream of an overall majority – and see the Greens, SNP and Plaid as enemies not allies.

Others may question whether Labour and the LibDems should even qualify as a ‘progressive’ parties, given that they fought the last election on pro-Trident, pro-austerity, neoliberal political platforms that put ‘clear grey water’ between them and the Greens, Plaid and SNP.

But if the logic of the position that Caroline and I are defending is strong, as I think it is, then we ought at least to try, and we certainly won’t succeed unless we try!

And there are historical precedents, that were no doubt similarly disparaged as pipe-dreams when they were first floated. The most striking such precedent is the 1906 pact with the Liberals that in effect enabled Labour to get into Parliament in the first place in numbers.

A more recent precedent is the little-known ‘non-aggression pact’ between Labour and LibDems which in 1997 was responsible for the scale of the destruction of the Conservatives, and in particular of the largely successful ‘decapitation strategy’ that they put into effect.

The unofficial pact, which involved Labour and Libdems not campaigning in each others’ target seats, received little attention in the mainstream press, but here is a rare mention of it in the Independent.

Others may ask, why exclude UKIP? Of course we should make common-cause with the ‘Kippers in relation to the undemocratic outcome of the 2015 General Election, and Greens have been doing that. But I believe a pact must involve a commitment to action on climate change, and UKIP stand diametrically opposed to any such idea.

So for all our sakes, it is vital that the ‘progressive’ parties open up now the question of working together. MPs, councillors, local party members, supporters, bloggers, trades unionists, citizens at large, all can create the pressure to make it happen.

And I can only agree with Caroline as she concludes: “I hope that Labour’s leadership candidates recognise that multiparty politics is here to stay – and I look forward to hearing how they’ll embrace the change rather than attempt, against the tide of history, to clamp down on it.”

Rupert Read was Parliamentary candidate for Cambridge for the Green Party in  the 2015 election, and remains Green Party national Transport Spokesperson. In his day job he’s Reader in Philosophy in the School of Politics, Philosophy and Languages at the University of East Anglia, and Chair of Green House.