At the dawn of the last decade, we saw a crushing defeat of Gordon Brown’s Labour Party, ushering in a devastating era of Tory-led austerity. It was the ultimate political price for the Iraq war and for 13 years of New Labour’s neoliberal policies, which alienated many of the party’s traditional supporters. As we enter a new decade, reeling from another terrible defeat, we must not repeat the mistakes of the past.

Make no mistake – December’s general election was a momentous defeat for our party and our movement which requires deep reflection, and there are no easy answers to why we lost. It is Labour’s worst election result since 1935, which has led some on Labour’s right to demand a shift to the so-called “centre-ground”.

We were led into that catastrophic loss by Clement Attlee, who went on to deliver one of Labour’s biggest ever electoral victories in 1945. His famously radical programme for government nationalised key industries, established the welfare state, and created the NHS.

Labour’s defeat means that none of the countless social factors behind the referendum result will be addressed for another five years. A Tory Brexit will do nothing to tackle decades of neglect and decline in parts of the country which lay behind the Brexit vote in the first place. If we believe (and I do) that radical left-wing policies offer a way forward, we need a debate about why we were unable to break through to the electorate.

Even many committed supporters of Jeremy Corbyn have acknowledged that he was an issue on the doorstep. But that must also be put in context: it’s hard to think of another British political leader in recent history who has faced such a barrage of attack from all elements of the media over such a sustained period. And, of course, much of this reflected the relentless attacks Corbyn faced within his own parliamentary party.

Behind these attacks was a wider agenda – to defeat and eliminate not just Corbyn but Corbynism, the idea that the left should pursue radical change. These are challenges which will face any Labour leader unless they are prepared to completely abandon any commitment to left-wing policies and make the Labour Party once again “safe” for the establishment.

It was Jeremy Corbyn and John McDonnell’s radically different policies which made them such a threat those in power. They had managed to finally shift the political debate away from a long-term neoliberal consensus.

They have facilitated debate on public ownership, public services, trade union rights, and tackling the climate emergency, in a way that was previously unthinkable in “mainstream” politics. For this alone they deserve our thanks and support.

The 2017 election saw Labour make gains by changing the conversation: by making the election about radical policy solutions rather than Brexit. It led to the biggest increase in Labour’s vote share since that momentous victory in 1945.

But it’s a formula we failed to repeat: we ultimately failed to make this anything other than a Brexit election, which inevitably ate away votes on all sides. Indeed, analysis from YouGov has shown that Labour lost as many votes to anti-Brexit parties as to pro-Brexit parties.

It’s inescapable that many of the seats lost were in working-class Leave-voting towns, and there are some who blame Labour’s defeat solely on its support for a second referendum. But to focus so narrowly ignores the swathes of other voters who we failed to convince.

The Brexit vote was, in part, a reaction to a failed neoliberal economic settlement, to years of austerity and decades of deindustrialisation. As working-class jobs in these communities have disappeared, the influence of trade unions and the Labour movement has waned.

Yes, their geographical history may be mining and unions, but it is not their present – and the Labour movement has not yet adequately analysed or debated the impact of these huge long-term social, economic and political changes. While the post-election debate about Labour’s lost working-class voters is essential, perhaps we also need a discussion about what Britain’s working class looks like in 2020.

As an affiliated union, the FBU enjoyed an unprecedented role in shaping Labour’s 2019 manifesto, helping to formulate a detailed plan to rebuild the fire and rescue service. But we also fought for a manifesto that would have reinvigorated trade unions, freeing us from decades of anti-union legislation, and ensured that Labour’s approach to the climate crisis was empowering to workers, with a socialist Green New Deal.

In the rushed timetable for Labour’s leadership election, the FBU will need to consider the policies and views of Labour leadership contenders – and there must be no retreat on policy. Whoever leads Labour into the next election must continue Jeremy Corbyn’s commitment to trade union rights, to public ownership, and to party democracy.

Above all else, they must be able to win back the working-class communities we have lost, both Leave and Remain. That will require a long-term strategic approach to build support in those communities for an empowering alternative to continued stagnation and decline – or we face another decade of Tory rule and the devastation it will bring.

Matt Wrack is general secretary of the Fire Brigades Union