Zac Goldsmith leaving Richmond upon Thames College in Richmond, London, after defeat in the Richmond Park by-election to newly-elected Liberal Democrat MP Sarah Olney. Yui Mok/PA Images. All rights reserved.On this day last year, the Liberal Democrats spectacularly won the Richmond Park by-election overturning a 23000 majority. So what? Well, this became the catalyst for the Progressive Alliance, which went on to contribute over thirty Tory defeats in the subsequent General Election – and could have put Jeremy Corbyn into No.10 if Labour had played ball just a tiny bit.

In seat after seat on June 8th the progressive vote outnumbered Tory support – but, in the end, the progressive vote was split, letting the right through. A Labour-led government could now be implementing the best bits of its and other manifestos. At worst we would be discussing the best possible Brexit and sweeping anti-austerity measures. With Labour still unable to pull clear of the Tories in the polls, and at least a medium if not long likely haul to the next election, will the Progressive Alliance have to play a part in the country’s political future again and, if so, how will it do this?

Just imagine this: Brexit in any shape leads to a new Tory leader and Prime Minister. Whoever it is, their message will be the same: ‘the future of Britain has been made. Whatever your views on the EU our fate is sealed and delivered. Our new place in the global order can only be secured by a party and a leader who wanted Brexit the first place, who sees and welcomes the opportunities for our nation. Now give me the mandate to lead our liberated nation into its golden new future – whatever you do, don’t hand it back to a divided and weak Labour Party’. In this scenario, are progressives going to fight each other – or the Brexit Buccaneers?

There is a deeper reason for a Progressive Alliance type of politics: how to build an alliance of ideas, policies, and forces that will see the paradigm shift to a new economy and a new society so many people are crying out for.

The quick backstory is this: in the aftermath of the Brexit vote, people across the left began to panic. With Labour polling in the doldrums, our world was slipping away. Surely now was the time to unite? The idea of a Progressive Alliance had already begun to resonate when Zac Goldsmith did what he said he would do by resigning his South West London seat over a third runway at nearby Heathrow. Cue the Greens’ courageous decision to stand aside and much pressure on Labour to do the same. They refused to relent, but through a plural campaign polled fewer votes than they have members in the seat. Zac was kicked out and here was proof of the concept that the Progressive Alliance could work.

But, instead of a hoped-for three years’ preparation, the nascent Progressive Alliance got only three months before being catapulted into the election and a defensive national campaign from a vertical takeoff. Even so, in over 40 seats the Greens stood aside and unprecedented levels of tactical voting helped engineer a close call election rather than a landslide. Tragically, Richmond Park was lost to the Tories and Zac Goldsmith as this time 5000 people voted Labour and the Lib Dem candidate lost by 45 votes. On a bigger scale, it looked like the return of two-party politics.

Is this, then, it for Progressive Alliance? There are two reasons why Labour and every progressive should hope the idea and practice of such an alliance isn’t allowed to fade away.

The first is electoral. No one now knows how or why people vote anymore. During the general election Labour MPs were contacting the Progressive Alliance desperate for deals, support and tactical votes – fearing they would lose slender majorities. In reality, they ended up with huge majorities. But what comes so easily, can go just as easily. Labour could continue to consolidate the anti-Tory vote or the 40% could splinter off the back of Brexit and the party’s lack of pluralism or commitment to proportional representation.

Some Greens will be warier next time, others will heroically vote and act tactically again. But whatever happens, the electoral field will become more volatile, not less. Furthermore, there are seats, especially in the south-west, where only the Liberal Democrats can defeat the Tories – so Labour needs them to win there. And government without the SNP still looks a forlorn hope. Given how high the stakes are going to be – will Labour stick with its all-or-nothing approach?

But there is a deeper reason for a Progressive Alliance type of politics. Trying to game our perverse electoral system in which hardly any voters ever count is sadly necessary. But the bigger issue is how to build an alliance of ideas, policies and forces that will see the paradigm shift to a new economy and a new society so many people are crying out for. To think that this can be done by one party, or one element of one party just feels inadequate.

Like the last big progressive shift in 1945, it takes a broad and deep coalition to make the leap to a new paradigm and then sustain it. That’s is why the ‘peace time’ successor to the Progressive Alliance is going to be called the Common Platform – a space for big ideas and the people practicing new forms of governance and production can help build the vision, policies, frames and networks for a new society.

A year ago today, the silver lining of Brexit was the by-election defeat of Zac Goldsmith. It inspired thousands of people to act and vote differently in the general election campaign – to work across party boundaries and to sacrifice party interest for a greater good. Once tasted, that spirit of pluralism is hard to forget. The 21st century will be defined not by old tribes but by fluid and agile networks that know their deeply held values of democracy, equality and solidarity can only be fully expressed by building alliances. Richmond Park was an outlier for a new way of doing politics, the ripples if which are just starting to play out.