On Friday 23 September, we launched our Green Guarantee to set out our role in that: a promise to members, voters and supporters about what it means to be Green. And at the heart of that promise is a new politics of public service that combines honest, consistent and principled Green opposition, with a willingness to do things differently and search for bold solutions.

We also have a message for the new Labour leader – stop wasting precious time on what divides you and instead invest in cooperation. Join us in making a persuasive case for doing things differently by looking to the future, not to the past. Commit to a progressive alliance.

With a snap general election looking increasingly unlikely, it seems Britain now faces three and a half years of a Conservative Government run by a Prime Minister who has, so far, done nothing to indicate she has a grasp on how to rise to the challenges we face. How to build a new resilient economy that values relationships rather than transactions. How to create a community immigration premium and the strong social connections that would allow us all to benefit from free movement. How to deliver smart, future facing, properly funded public services run by the people for the people. Nor has she risen to the biggest challenge of all – a world unlimited by climate change.

A one-off general election alliance between progressive parties to try to prevent the Conservatives forming the next government could be a game change. That’s why our Green Guarantee contains a pledge to cooperate rather than compete, if it will deliver the best future for Britain.

Such an alliance is, critically, also an opportunity to unite behind a pledge to replace our outdated voting system with a citizens’ democracy. In 2015 more than 1m people voted Green and they deserve to have their views represented in Parliament by more than one MP. Almost 2m voted Lib Dem and yet they have just eight seats, while almost 4m Ukip votes claimed one MP. If we want a future where decisions are negotiated, not imposed, where power and wealth are redistributed, fair elections are essential. And if we genuinely want to heal the divisions revealed by the EU referendum campaign, to tackle the fear, inequality and hopelessness that’s been laid bare, we need every voice to be heard and every vote to matter.

Taking back control means having a second referendum on the terms of any EU deal. It means we need to be clear what we would like our future relationship with the EU to look like, what we’ll be negotiating for, and Parliament having a full debate and vote on triggering Article 50. And it means a general election to decide who delivers the deal.

Our Green Guarantee puts the principle of working together to solve common problems at the heart of any agreement – we still think this is the best way to protect our environment, workers’ rights and free movement. In this age of insecurity, collaboration and partnership matter more than ever before.

They also underpin the innovative Green economy of tomorrow. A sharing and participative economy where the exploitative Uber model gives way to a taxi firm owned by drivers and passengers. An economy for the digital age where modern technology and a universal basic income allows us to live larger lives, and where work is about real purpose, not a means to an end. An economy that’s jobs rich, energy efficient and really means business.

Our Green Guarantee is that, as co-leaders of the Green party, we will embrace the rapidly changing uncertain world in which we live, not turn from it. Be brave enough to map the future, not simply react to it. We invite whoever is elected as the new leader of the Labour party to do the same.