With all eyes fixed on the battle for the so-called ‘red wall’ of Labour strongholds, it’s easy to forget no so long ago everyone in politics was talking about the ‘green surge’. 

Sian Berry’s Green Party is swimming against the two-party tide in this Brexit-dominated election, but she is hopeful of gains when voters go to the ballot box on Thursday – and the co-leader has every reason to be ambitious. 

Her party recorded its best ever results in local and European elections this year and the Remain alliance deal struck last month has seen Greens, Lib Dems and Plaid Cymru stand aside to help each other in 60 seats.

A renewed focus on climate change, thanks to campaigners like Greta Thunberg, David Attenborough and those inside Extinction Rebellion, should be a boost, and well-liked media performers, like Caroline Lucas and Yorkshire refugee turned city mayor Magid Magid, on camera helps too. 

With Labour stealing Berry’s thunder with its £250bn green new deal, however, the reality is that the party’s limited resources will be focused on a handful of key targets, most notably Bristol West where high-profile local activist Carla Denyer is standing. 

But this close-run election, largely fought between Jeremy Corbyn and Boris Johnson, could go down to the wire. It is not beyond the realms of possibility that one or two Green MPs could hold the balance of power. 

Speaking to HuffPost UK at the party’s London HQ at Bermondsey’s Biscuit Factory, Berry makes clear she will not enter an official coalition, but says her MPs’ support for Corbyn would come at a price. 

Berry would ask Corbyn for the immediate scrapping of first-past-the-post voting system, without a referendum, in favour of proportional representation (PR). 

“At the moment, the system is broken – there’s no question,” she says. “We have a system where votes don’t match representatives. It’s not a real democracy.” 

Amid calls for Corbyn to resign, Berry says leadership after December 12 is a “question for everybody” but stresses her party would ask for “practical things not personal things” in any deal that allowed Labour to govern. 

Berry dismisses Johnson’s claim it would be “a coalition of chaos”, underlining that all parties had worked together to hold the Conservatives to account over Brexit. 

“We’ve learned quite a bit from the final throes of the last parliament,” she said. “The parties were working together much more coherently on things like amendments to bills. 

“Towards the end, when we were short of time, there was much more cooperation and parties were looking forward. It’s a terribly tribal system, but we now have some experience of having worked together.” 

She added: “I think all the grown ups are at least all on the one side.”

Berry, who will next year challenge Sadiq Khan in the London mayoral race, is also keen to push her party’s other policies, such as a universal basic income of £89, adding misogyny to hate crime legislation and writing off student debt. 

On Labour’s green offer, Berry says “they’re nowhere near us – nowhere near”. 

The Greens would spend £100bn a year on cutting emissions, plant 700m trees by 2030, remove fossil fuels from the economy and build 100,000 zero-carbon homes. 

For Berry, there is no time to waste when it comes to climate change and, unlike rivals’, their 2030 net zero carbon target is an absolute deadline rather than an ambition. 

The UN’s Intergovernmental Panel on Climate Change (IPCC) in its 2018 special report stated that food, water, and land would be at risk if people did not “drastically” change the way they lived by 2030. 

“I think it really does qualify as our final warning, it’s ten years’ away and we’re arguing about whether or not we can get it done by 2030,” she said. “We genuinely have to start right now.”

She added: “This makes me terrified because the politicians we are about to elect are the last ones who can deal with climate change.

“We can’t wait for Greta Thunberg’s generation to grow up and hand it over to them. We have a responsibility to them to set these wheels in motion.” 

Berry, who graduated with a masters in engineering from Oxford and spent her early 20s working in industry, says she is dismayed by how politicians, and often older people like Jeremy Clarkson, treat campaigners like Thunberg  

“It is a very patronising attitude, you know like ‘she can’t possibly know what she’s talking about’ or ‘why should we listen to her’.

“To be honest, it’s the exact attitude I’ve had to myself throughout my life. it’s not different. You get older than 16, and if you’re saying these things, people still patronise you.” 

Berry lights up talking about possible progress in the election, admitting “it’s hard to make predictions because the polling is very volatile” but picking out Bury St Edmunds, the Isle of Wight as possible gains. 

She said: “Everyone in Bristol is really fired up to win our second MP. Bristol ought to be as lucky and special as Brighton in having a Green MP.”  

Berry is among many politicians on the left to warn of potential dangers to the NHS in a post-Brexit US-UK trade deal.

She said the protection of NHS data from American firms should be a particular concern, adding: “Think in terms of what people then know about your health and your history.

“If we move to an insurance system and you’ve got pre existing conditions, you’ve got risk factors and a [health] history and they [companies] want that data so that they can discriminate and pick and choose the people they insure.  

“Look at the problems with people in America with people who can’t get insurance. It’s sometimes not that they can’t afford it, it’s that they can’t get it. 

“We have the NHS. It is our universal system is paid for by everybody because it’s a common good and that is the principle in the system.” 

She also believes the US would have the “largest possible incentive to have more control” over the supply of drugs. 

Berry also hits out over the “clear alliance” between Johnson, Donald Trump and Nigel Farage. 

“It’s not just that Trump will get to do an uneven trade deal with us, it’s that he’s trying to advance the cause of separatism and the authoritarian right in Europe. 

“He thinks that the Brexit is a route to that.” 

Berry insists, however, that a universal basic income would be “transformational”. 

Under the Greens’ plan, all welfare but housing benefit and carers’ allowance would be cut and each citizen would be paid £89-a-week regardless of pay or position. 

Berry says scrapping any means testing of benefits and “simplifying” the tax system would turbocharge equality, and insists it would not disincentivise work despite test areas in Europe throwing up mixed results. 

She admits higher earners would pay more but claims means testing discriminates against minorities and the relatively low £89-a-week payment did not remove the pull of employment. 

“There’s a there’s a reason why Martin Luther King said that basic income was the next step in the civil rights movement, because it removes so many opportunities for discrimination to lead to worse outcomes,” she says. 

The election is also voters’ chance to end austerity, though Johnson has backed a new spending programme for public services. 

“Austerity has had 10 years now, and it is biting,” she says. 

“There’s more and more people families falling off the end of the edge of the cliff edge of housing and into homelessness because nothing, nothing is fixed. 

“And that is only going to get worse and worse and worse. So, we have to reverse austerity, as soon as we possibly can.” 

This election is “literally a watershed”, she adds. 

“We go one way or the other. And if we go the start going the wrong way, even for a few years, especially on climate then things are going to be almost impossible to pull back.”