For two and a half years, British politics has been a pantomime played out in the corridors and boardrooms of Westminster and Brussels. The electorate has barely managed to press their noses against the glass and peer in: much of the Brexit debacle has unfolded out of sight and scrutiny. Instead, ever since Boris Johnson’s ascent to the premiership, the country has effectively been treated to a one-sided general election campaign; the opposition has been all but squeezed out of media coverage. All of this now changes: the spectators can storm the stage.

In the 00s, it was often claimed that political apathy had replaced political participation. Membership of political parties and electoral turnout were both said to be in irreversible decline. Who can bemoan the lack of political participation now? This is our age of mass politics: the Scottish independence movement, Farageism and Brexitism, a youth-led climate emergency movement, and Jeremy Corbyn’s Labour, which began as a husk and flowered into western Europe’s biggest political party. And it is this, in large part, that makes the election so unpredictable, so volatile. There is a politicised populace united around a single but fundamental point – desire for rupture with a status quo that never enjoyed enthusiastic support and now has lost popular acquiescence. If Johnson triumphs, his government will wrench Britain out of the EU with a deal that threatens to punch a hole the size of Wales in the economy, and use Brexit to remake British society in a hyper-Thatcherite mould. Labour’s mission, on the other hand, is to up-end a generation-long experiment in market fundamentalism and redistribute wealth and power away from its principal beneficiaries. Each represents an abandonment of the old order, even though the Tories’ version will benefit the vested interests who bankroll them.

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The Tories’ strategy is clear: use Brexit to torture Labour by dividing its electoral coalition and drowning out its domestic agenda. Their secret weapons are Jo Swinson’s Liberal Democrats, who they hope will siphon enough votes from Labour to deliver scores of marginals to the Conservatives – even though Labour is now the only major party committed to a referendum with remain on the ballot paper. Most of the British press will act as Johnson’s cheerleaders, and the Tories’ traditional donors – hedge fund managers, financiers, magnates – will keep them flush with money.

But it is mass politics that presents the party with a challenge. After MPs voted to approve a December election, the grassroots pro-Corbyn Momentum movement launched an appeal to raise £50,000 in 48 hours; instead, it raised £100,000 in the first 12 hours, twice as much as in the same time period in 2017, and with an average donation of £24.40. It belies claims that enthusiasm for the Labour leadership has collapsed among a demoralised membership. And if that commitment to part with money is matched by a willingness to knock on doors, the party will be able to partly bypass an overwhelmingly hostile press and talk to voters one-on-one.

It is mass politics, too, which challenges the Tories’ ability to monomaniacally focus on Brexit at the exclusion of all else. Polling shows that the environment has risen dramatically as a political priority for voters since January: a new poll finds that two-thirds of Britons believe the climate crisis is the biggest issue facing humanity, with more than half declaring that it would affect how they voted. This is, in part, down to protests by the Youth Strike 4 Climate and Extinction Rebellion. Labour’s radical policies for a Green New Deal – which link tackling the climate emergency to creating jobs, overhauling public transport and improving living standards – have yet to cut through. But in an election campaign, we can expect there to be an appetite to hear such proposals.

Johnson’s strategy is to distance his administration from a lost decade of Tory rule. That deception cannot be allowed to pass. And he must now contend with how those nine years have politicised large sections of the electorate. Wages are still lower than they were before the crash. Parents have been roused to protest over the slashing of per pupil funding. As homeownership collapses, and council housing stock has been sold off en masse, an entire generation has been driven into a private landlord sector where rents are extortionate and security absent. As cuts to benefits have expanded from disabled people to the low-paid, attitudes towards social security have transformed, with most no longer deeming entitlements as too generous. It is for Labour to pin the blame for these crises on Johnson and his colleagues, and to portray attempts to shift the conversation away from them as arrogant Tory indifference. Brexit itself cannot necessarily serve as the distraction Johnson desires, either: in the last pre-election prime minister’s questions, the Tory leader was left rattled by Corbyn’s focus on the risk of the NHS being flogged off to US multinationals under a Trump trade deal.

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But focusing on the misery of Tory Britain is a trap. Instead, Labour’s campaign should exude a relentless optimism: a sense that a nation this wealthy has the resources to overcome every injustice and challenge if the willpower is there. The age of mass politics is one that demands radical solutions rather than tinkering. Labour may begin the campaign with dire polling, but Tory despair under Theresa May has given away once again to hubris. The movements and struggles of the last decade have politicised millions to demand a breach with a failing social order. It is that resurgence of people power that Labour must tap into – and which Johnson’s Tories should surely fear.

• Owen Jones is a Guardian columnist