Many Labour members, and indeed many of us from other political parties, will be relieved to see Jeremy Corbyn taking part in the first official Labour leadership hustings tonight. Corbyn is different from the other candidates for obvious reasons. He has been an outspoken critic of government cuts, opposes Trident, has been a respected voice of reason on foreign policy, and recognises that addressing climate change is a way out of our economic crisis, not a distraction from it. His candidacy ensures these critical issues will be on the agenda.

But whoever takes over the reins of the Labour party needs to recognise that, if Labour is to increase its relevance and appeal, it needs to become a movement that embraces the energy and vibrancy of all those who support a progressive, multi-party politics, both inside political parties and in our communities. This must include support for a fairer voting system, a commitment to genuine engagement with voters, and an open mind, at least, on locally agreed electoral pacts. It’s certainly a challenge, but an entirely different type of politics could be the result.

So my question to candidates taking part in tonight’s hustings is this: will you be part of this new multi-party politics for Britain?

Before the next general election, those of us promoting a more progressive politics must think long and hard about how we achieve it, given the longstanding opposition to electoral reform from the majority of both Tory and Labour MPs. First-past-the-post is designed to keep power in the hands of the few – it’s clear that we need to hack the system before we can change it.

One strategy – which is my personal view and on which I would value contributions from others – might be to consider the potential for progressive pacts. A possible first step could be for Labour, Greens, Lib Dems, the SNP and Plaid Cymru to empower local branches with the ability to back candidates from other parties if they wish.

Secondly, and in a transparent and open way, those of us who want progressive pacts could set out a core set of pledges that parliamentary candidates must follow if they want cross-party support. No doubt, for a local Green party to back a candidate from another party, that candidate needs to commit to serious action on tackling climate change, recognising that we must live within ecological limits, and take a very firm stance against further austerity and the selling-off of our public goods. Crucially, local voters would need to have their say and be properly involved – they’re the ones who should be the ultimate beneficiaries.

Labour, Greens, Lib Dems, the SNP and Plaid Cymru could empower local branches to back candidates from other parties

But a prerequisite for a progressive politics of the future must be an acceptance that we desperately need a fairer voting system for general elections. As the sole Green party MP – despite more than one million people voting Green in the last election – I’m aware that my calls for a fairer voting system may sound self-interested. But it’s time for Labour in particular to realise that if it wants to call itself “progressive”, it cannot stand for an electoral system that systematically marginalises the vast majority of people’s views – and hands supreme power to a party that 76% of people didn’t vote for.

Moreover, the result in Scotland, where Labour won 700,000 votes but only one MP, must surely be a loud enough wake-up call that our broken electoral system can no longer be relied upon by Labour, even in purely self-interested terms. It’s worth noting here that the SNP, which benefited so significantly from first-past-the-post, continues to back a proportional voting system for Westminster.

I do not pretend to offer a complete solution to our political malaise, and I recognise the challenges inherent in what I’m setting out. For example, many Labour or Lib Dem candidates wouldn’t get approved by a Green party meeting, or vice versa. But what I cannot be more sure of is the fact that those of us who are serious about addressing the climate crisis, or halting and reversing the destruction of our welfare state, must find a way to work together – and do so quickly. In the grim context of accelerating climate change and deepening austerity, and when one in five families say they’ve already had to cut back on food because of child benefit changes, the need for a new progressive politics could not be more urgent.

I hope that Labour’s leadership candidates recognise that multiparty politics is here to stay – and I look forward to hearing how they’ll embrace the change rather than attempt, against the tide of history, to clamp down on it.