There’s been some debate recently, on these pages and elsewhere, about the Green party’s role in politics. Last week Owen Jones – a political ally of ours on many issues – suggested we should consider affiliating to the Labour party. With Labour’s membership at record levels, there are renewed calls for “one last heave” to get Jeremy Corbyn into No 10.

But we’re not going to affiliate to the Labour party. The reason is simple: ours is a different political project to theirs, and we believe in a plural, progressive politics.

To understand the differences between our parties, let’s be specific for a moment. Imagine this: a shadow cabinet meeting that included a Green party MP, as Owen Jones suggested. Could we sit there and take collective responsibility for backing Trident’s replacement – something which we don’t just oppose on cost grounds but on principle? The answer, of course, is no.

Politics is often about compromise, but it should also be about parties being true to themselves. While we might have stood alongside Jeremy Corbyn and John McDonnell on anti-austerity marches for many years, we part with them on many key issues – from privacy and policing, to what’s at the very heart of our own politics: protecting our environment.

Despite our rotten electoral system, the Green party won more than 1.5m votes in the last two general elections combined

The world we want to create is about much more than economic fairness. We ask fundamental questions about who the economy and the world’s resources are for. We exist to challenge economic orthodoxy: to say that people should not be shackled to a system, to work more hours in jobs they don’t like, to buy more stuff they don’t really need. Labour for labour’s sake is not something we sign up to. It’s about seeing true wealth and wellbeing in more than monetary terms, which the safety net of a universal basic income would help guarantee.

Across almost all other parties, there is a consensus in favour of indiscriminate economic growth across every sector of the economy. But this isn’t the Green – or for that matter, real – solution to the problems we face. Indeed, we believe it’s a major cause of them.

Neither have we given up on staying close to Europe – which is why we continue to push for a people’s poll on the final deal, in which we would unapologetically campaign to remain. It’s not that we don’t understand where Labour is coming from, we just think that they are wrong – and that’s OK.

Our tactics are different, too. One hundred years after the suffragettes won the vote for some women, we’re also redoubling our commitment to the many brave people taking peaceful direct action in this country. For us, progressive politics has never been just what happens in council chambers and parliaments. We pride ourselves on being a voice in politics for social movements and protesters, whether that’s those doubling down against fracking or the courageous hunger strikers at Yarl’s Wood.

Being a Green party politician isn’t always a glamorous pursuit – and it’s certainly no fast track to holding political office. But what we do has a big effect, whether that’s opposing austerity after the financial crash, saying the unsayable on drug law reform, or being the first movers in the soon-to-be-successful fight against fracking.

Despite our rotten electoral system, the Green party won more than 1.5m votes in the last two general elections combined – and we’re not planning on sitting out the next one. If Labour are serious about building bridges with other parties, they should join us in pledging to ditch first past the post, and replace it with a fair voting system. The Green party has always been committed to working across party lines – but we’re not about to be folded into the Labour machine.

• Jonathan Bartley and Caroline Lucas are joint leaders of the Green party