If Theresa May fails to secure a landslide on June 8, the heroism of the Greens will deserve a big chunk of the credit. The party has stood down in 31 seats. This will make it easier either for candidates from rival parties to capture Conservative seats or defend themselves from a Tory attack. (See below for the two lists of seats being attacked and defended).

Sadly, the other main “progressive” parties haven’t played ball. No Labour candidate has stood down. This is despite the Greens standing down in 10 seats which Labour is defending against the Tories and seven where it is attacking them. Labour even expelled some of its activists for campaigning for the National Health Action candidate who is seeking to unseat Jeremy Hunt, the health secretary, in South West Surrey.

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The Liberal Democrats are barely better. They have stood down in only two seats where the Greens are fighting the Tories – Brighton Pavilion, where Caroline Lucas, its co-leader, is standing – and Skipton and Ripon. The Greens, by contrast, are stepping aside in four seats where the Lib Dems are being pursued by the Conservatives and a further eight which they hope to win from the government.

The small Women’s Equality party did take some action. It is not putting up candidates in three seats where the Greens are facing off against the Tories – in return for the Green’s standing down in Shipley, where Sophie Walker, the Women’s Equality leader, is seeking to unseat a Conservative.

However, the failure of Labour and the Lib Dems to play ball means there are far fewer progressive alliances in this election than there could have been. Unsurprisingly, the Greens were reluctant to keep standing down when they were getting so little in return. In some cases, they also didn’t endorse another progressive candidate even when they stepped aside.

Progressive and pro-European aren’t quite the same

Being progressive and pro-European obviously aren’t the same thing. But there’s a huge overlap. Of the 19 Tory seats being challenged, only Twickenham is held by an MP who has publicly voted against parts of May’s Brexit policy since the referendum. And many pro-Europeans would still prefer the Lib Dem challenger, Vince Cable, to win against the incumbent Tania Mathias.

So, in general, progressive alliances have advanced the pro-European cause this election. Look at the Lib Dems. Not only will four seats already held by the party now be easier to defend; in three Lib Dem targets, the Greens got more votes in the last election than the size of the Tory majority. In other words, if the only thing that changed since 2015 was that Green voters moved en masse to the Lib Dems, the Tory candidate would be kicked out in Lewes and St Ives, as well as Twickenham.

Similarly, Labour will now find it easier to win 10 seats such as Ealing Central and Acton, where the strongly pro-Remain Rupa Huq is defending a wafer-thin 274 majority. There’s also one Tory seat, Bury North, where the Greens got more votes than the size of the Tory majority. Labour’s chance of winning this has risen because the Liberal Democrat candidate is now urging activists to support the challenger to prevent the Tory being re-elected.

Indeed, the Lib Dem candidate’s endorsement in Bury North could be the next stage of pro-European and progressive politics. Even when candidates don’t step down, they can still decide not to fight their seats aggressively to avoid splitting the vote. Compass, the pressure group that has been campaigning for progressive alliances, is holding an event in London on Monday to advocate precisely such non-aggression pacts.

That said, divisions in both the pro-European camp and progressive politics have led to many missed opportunities. For example, the Green’s challenge against a Brexiter in the Isle of Wight seems set to fall flat because the party will have to fight off both Labour and the Lib Dems.

Equally, Clive Lewis, who quit the shadow cabinet after Jeremy Corbyn called on all Labour MPs to back Article 50, may now be vulnerable to the Tories because he will have to split pro-European votes with the Greens and Lib Dems. The fact that UKIP isn’t standing in his Norwich South constituency makes him particularly open to attack.

Kate Hoey, the ardently pro-Brexit Labour MP, also looks likely to be reelected as a result of a three-way split between pro-European parties in her Vauxhall seat. Here, too, UKIP isn’t standing. Indeed, its collapse as a party – it’s not contesting 247 seats – suggests that Britain’s pro-Brexit forces are better at joining forces than its pro-European ones.

Correction: the Liberal Democrats stood down in two seats, not one as originally written. The piece was updated on May 20 to reflect this.