This was a bittersweet election. We rejoice at the fact the Conservatives have been pegged back and the landslide they presumed was theirs by right has been denied them. We are delighted that an alternative to austerity and nearly 40 years of free-market fundamentalism has secured 40% of the vote. We celebrate the exuberance and scale of the youth vote and both feel an incredible duty to repay their faith in us and our colleagues. And we are proud that in some key marginals cooperation not to split the progressive vote resulted in the Tories losing.

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But equally we felt a profound sense of frustration and dismay when Tories won by narrow margins in places such as St Ives, Richmond Park and Hastings – it really could have been so different. In seat after seat, progressive votes were wasted, because of our broken electoral system. If every progressive voter had placed their X tactically to defeat the Tories then Jeremy Corbyn would now be prime minister with a majority of over 100.

Electoral alliances, which in this instance saw people across parties cooperate on tickets that included support for proportional representation and the common goal of preventing Conservative candidates winning, were pulled together quickly for the snap election. There wasn’t time to build deep relationships at either the top of the parties or more importantly on the ground. They were not perfect nor, in many instances, were they more than loose arrangements around tactical voting. However, more than 40 local alliances were formed, where almost exclusively Greens put the national interest before their party. It had a huge impact on the vote – more than doubling the average swing away from the Tories.

But just as important as the vote was the cultural effect of people from different parties working together to a common aim. This was about doing politics differently and it’s not just election results that are the measure of success. It’s the numbers of people who knocked on doors for the party most likely to beat the Tories, who came out and got involved in an election campaign for the first time ever, and it’s the sense that politics has become something hopeful and positive again. People in Britain have embraced a more plural and open politics and it’s critical that what happens next continues to build that vision and listen to their voices. To do otherwise would be both a massive disservice to democracy and to misunderstand that the Corbyn effect is just one wave in the tide of change.

During an election campaign everything inevitably becomes very transactional – it’s about seats, candidates and votes. But we shouldn’t forget the challenges we face – of markets that are too free and a state that can be too remote, a democracy that still leaves so many voices unheard and, of course, climate change on a scale our people and our planet simply can’t cope with. It is going to take a politics that is social, liberal and green to overcome these challenges. No single party or movement has all the answers. We are going to have to learn to cooperate as well as compete to build the society of which we dream. And we are going to have to recognise that the future is not a two-party system but one in which smaller parties grow – both in influence and in their electoral representation.

Indeed, this is exactly the mood of the millions of young people who voted. They live in a world of social media in which their identities and allegiances are permanently in flux. They like and they share. They flock to one idea, group or party and then another. We need a politics that is purposeful but also as responsive, open and collaborative. We can and must fight many things: inequality, climate change and our democratic deficit – but what we can’t fight is the collaborative culture of our age. Instead we must bend this new collaborative modernity to our values of equality, sustainability and democracy.

We can’t forget either that the Tories will do their utter cynical best to hold on and regroup to maintain their grip on power. And in the face of that, the sheer scale of alliance and tactical voting this time cannot be taken for granted. Support and votes were lent to Labour, but people can and will take their votes back if they don’t see a new politics emerge.

So what next for electoral alliances? A whole group of MPs have felt their benefit and must now work together in parliament on a cross-party basis so we can build a progressive relationship with Europe, make the case for electoral reform, tackle the environmental crisis and establish the basis for a post-austerity and post-neo-liberal economy. The regressive alliance we see forming before our eyes between the Tories and the DUP can only be fully countered by a progressive alliance on the opposition benches. On the ground, party activities who have tasted this more collaborative future are going to want to set up local electoral alliance groups, not just for electoral purpose but to work together across all parties to make change happen where they live.

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Some will want to believe that what we have seen in this election is the reversion to two-party politics. That misreads the mood. Yes, the Labour party has been the main beneficiary of the hunger for change in our country, but this doesn’t mean Labour alone owns it. Politics is now so incredibly volatile and complex. If progressives want to win big, not just to peg the Tories back, or be in office for a short period to ameliorate the worst excesses of free-market economics, then we must build a permanent and vibrant progressive majority for change. One in which diversity is seen as a strength and no party has a monopoly on your vote.

We are from different parties and different political traditions – and we celebrate that because, while we share so much, we can learn much more from each other. If we work together there is nothing progressives can’t achieve. The limits of the old politics are there for everyone to see – the limitlessness of the new we are just starting to explore.