Is the Labour party dying? It’s a question that commentators have asked since the devastating election defeat last week. But in fact, as a party of working-class self-representation, Labour is already dead.

Throughout much of the 20th century, there were parts of northern England where jobs came with firm expectations about Labour party membership. Labour, the unions and the nonconformist churches were the great social institutions of 20th-century working-class politics. Secularisation in the 1960s saw the decline in the role of the church. Then the unions were dismantled in the 1980s. Now the Labour party, as we once knew it, is gone. Constituencies that had been held by Labour almost since the modern two-party system was born – such as Don Valley and Wakefield – have voted in the Tories.

Change does not happen overnight. The roots of the present defeat take us back several decades. Labour’s dramatic victory of 1997 was built upon a shift in the composition of the Labour vote: more middle class, more concentrated in the home counties. In the 2000s, Ukip’s rise was widely seen as a threat to the Tory vote. But as Robert Ford and Matthew Goodwin documented so well in Revolt on the Right, Ukip was also starting to erode the working-class Labour vote. It shifted from its origins as an anti-EU party, criticising instead the government’s commitment to an open labour market and its embrace of EU free movement rules. Lacking real debate within Labour, the immigration issue became a symbolic one for voters, exemplifying the detachment of the London leadership from grassroot concerns.

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Ideologically, Corbynism was a break from New Labour centrism but sociologically, it was more Blairite than Tony Blair. As the Labour MP Jon Cruddas has argued, the Corbyn revolution in the Labour party has narrowed its social base even further, making it the party of young, middle-class southerners, popular in London and some prosperous university towns.

A final nail in Labour’s coffin has been Scotland where, for different but not unrelated reasons, the party has lost almost all its seats. The collapse of the Scottish Labour vote over the past decade is one of the great electoral shifts in recent times, making the geographic retrenchment of the party’s vote in England all the more damaging.

The Labour party grandees currently reflecting on why the 2019 election went so wrong have been quick to blame Brexit. This is too easy. Brexit was both catalyst and cause. The Labour party’s response to the 2016 referendum reflected the sociological changes already under way at the heart of the Labour movement. Labour leave voters were concentrated in those parts of the country that were of little interest to many of the activists driving the party forwards.

Inevitably, this lack of interest was reflected in how the party responded to Brexit. Some – including Jeremy Corbyn himself – were sympathetic to an old-school left Euroscepticism of the kind articulated by Tony Benn. But that tradition has died within the party. Much of the party leadership and its membership believed that Brexit was evidence of working-class xenophobia and a general ignorance of all things EU-related.

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There were some MPs, such as Caroline Flint, who warned against this and stood out as Labour defenders of the referendum result. But after a protracted struggle, ardent Labour remainers succeeded in making a second referendum a party promise. After three years of leave supporters being dismissed as racist and stupid, and seeing Labour eventually get off the fence and back the People’s Vote campaign, how on earth did the party expect its leave supporters to react?

Brexit was also a cause in its own right. It pitted a dogged commitment to the politics of democratic consent against an ideologically charged promise of socialism in one country but at the cost of negotiating a softer Brexit and rerunning the EU referendum.

For leavers, Brexit has always been about more than just policies. Membership of the EU denoted a fundamental change in society – a movement from being a nation state to being a member state. Governments increasingly seemed to be getting their legitimacy and sense of purpose not from their voters but from their association with other governments across Europe. Over time, a gap opened up between politicians and voters. Many people felt as if it didn’t matter who they put in Downing Street – they still had little say over the country’s governing structures or the most important decisions that shape society.

The current Labour leadership was often portrayed as dogmatic Marxists but on Brexit they demonstrated an incredible willingness to compromise on the question of rule by democratic consent. Because of what Brexit meant to them, voters were far less willing to compromise. When Theresa May first brought her withdrawal agreement to the House of Commons, the near-unanimous response by the British left was to reject her deal. Labour’s fate would have been very different had the policy instead been to accept the result of the 2016 vote, support her deal and then push for a post-Brexit election.

British politics post-Brexit will not be any kinder to Labour. With the social structures of Labourism in the north of England and in Scotland now in terminal decline, there is every possibility that the Tories will hold on to the new seats they won last week.

As an indication of what may lie ahead for Labour, it is worth looking across the Channel. On the Rue Solférino, a stone’s throw from the River Seine, stands the historic headquarters of the French Socialist party. It was recently sold off and converted into luxury flats.

• Chris Bickerton teaches politics at Cambridge University and is a founding member of The Full Brexit