“If it’s a one-off electoral alliance to increase the number of MPs that support proportional representation then dissolves again once we have elections based on PR then I’m happy with it," said Ian, a man in his sixties from the East Midlands who joined the Greens after leaving Labour three years ago and preferred not to give his surname. “I think there’s a real issue of losing our identity and being seen as Green-tinged Corbynistas."



Chandler, a teenager who was sitting next to him, agreed, saying it was too risky: “I don’t really want to get into a progressive alliance or anything with Corbyn because I feel like that would hurt the Greens, and we could end up like the Lib Dems with the Conservatives, or it could make the party split in a way, like how Labour’s splitting under Corbyn."

Conscious of those worries, Bartley was keen to explain that the electoral alliance would be a “one-off electoral arrangement for one general election, in probably a handful of marginal Tory seats where we think we can work together to get the Tories out to form a government which can then implement PR".

Still, such an agreement would require a degree of camaraderie, which was somewhat lacking in Birmingham. During their acceptance speech, Bartley pointed out that when the Greens disagree with each other “we don’t throw bricks through one another’s windows”, while Lucas said they stood “here more united with two leaders than some parties are with one”.

Talking to BuzzFeed News, Bartley even urged wavering left-wing supporters to consider their options: “In the Green party, policy is decided democratically, you can call the shots in terms of political agenda on things like basic income, and you can also set the policy in the Green party.

“In the Labour party, you’re not quite sure who sets the policy and if the policy is set, who’s going to support it and who’s going to implement it, and certainly when it comes to votes in the House of Commons, who’s going to actually vote for it.”

Lucas added: "Whether it’s nuclear weapons, whether it’s nuclear power, whether it’s electoral reform, with the Green party you know what you’re getting."

There is also no love lost for Labour among Green members; when asked if he’d consider joining a left-wing Labour party led by Corbyn, Liverpudlian activist James laughed for around seven seconds straight.

After catching his breath, he explained: “They’ve all been brawling and in-fighting, it’s so unattractive. Nobody wants to see them doing that. Actually you’d want politicians to be saying ‘well, people have just voted to leave the EU so here’s a plan', 'actually there’s refugees trying to cross the Mediterranean, here’s a plan'. It’s so childish."

Labour’s lack of discipline worried many other members; Ian, mentioned earlier, said he used to be a Labour member but that the party now reminds him “too much of factions in smoky rooms rather than building [support] in communities and working with people”. Focusing his attack on the pro-Corbyn group currently helping run the leadership campaign, he said that “Momentum’s meant to be the mobilising force but it mobilises internally to win debates, not to win campaigns and communities.”

Another member, a man in his twenties, described himself as “actually quite Corbyn-sceptic”. “I just can’t look at the polls and not see the fact that he’s driving them off a cliff," he said, and though he used to be a Labour member, “I’m not much more likely to go over to the Labour party now, when it’s falling apart."

While not fundamentally against having a progressive alliance (“I think it’s a great idea in principle”), he thought “the practicalities of it are going to make it impossible, partly because both parties are actually a lot more tribal than we realise”. He added: “There’s a lot of people in the Green party who think we’d be selling out, and there’s a lot of people in Labour who think they could win without us."

The other issue is geography: Though Bartley did say that the alliance would only be focused on certain seats, Green activists in Labour’s heartlands didn't seem convinced.

“In Liverpool, Labour have dominated for so long and they’re not very effective, they’re not very grassroots, and they’re not really listening to the people they represent any more," James told BuzzFeed News, “so I couldn’t possibly see myself doing a deal with local Labour in Liverpool."

Keith, a Welsh member who joined last year, agreed: “In Wales it’s about getting Labour out, not doing deals with them. We’re more like to do deals with Plaid Cymru than the Labour party, because they’ve been so entrenched in the assembly, for 18 years now – that’s who we want out."

In her first speech as co-leader Lucas herself admitted that the Greens and Labour would have to switch from opposing each other to working with each other: "Lambeth in south London, where Jonathan comes from, Greens have been battling a Labour council that is ignoring local people. It’s closing libraries and destroying people’s homes and communities."

With such a potentially unstable partnership ahead of them, the Greens may need to offer more to Labour if they want to get its help in order to bring about PR.

Lucas does have an argument that may appeal to Corbyn’s camp, but not one it would like to hear: PR tends to offer fairer election results to parties not polling high, and Labour may be becoming one of them: “I think increasingly it’s going to be in Labour’s own interest to promote electoral reform," she said. "If you look at Scotland, where they’ve got nearly 25% of the vote and only one MP, it’s not working for them either."

If all else fails, or a later leadership challenge eventually unseats him, Corbyn shouldn’t worry – asked if he’d consider jumping ship and joining Labour, an activist who’s been in the Green party for 30 years said: “Jeremy doesn’t strike me as much of a leader, unfortunately, but we’ll take him in if he wants to jump the other way."