The battle in Labour marginals will decide the scale of Theresa May’s victory – and working-class voters increasingly back her

Theresa May first made clear her ambition to rebrand the Conservatives as “the workers’ party” in her first speech as prime minister to the Tory party conference in 2016.

In that speech the comprehensive-school educated May’s repeated emphasis on “ordinary, working-class people” was taken as an attempt to break from the class-limited appeal of the public schoolboys in David Cameron’s cabinet.

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Her insistence that she would “govern for the whole nation” and her claim that “we are the party of the workers” was backed up by an explicit early commitment to guarantee all existing EU legal rights in British law so that rules and protections for workers would apply after Brexit as they did before.

The latest polling data shows her hopes of claiming to be the workers’ party have been realised far earlier than she could ever have expected.

For Jeremy Corbyn appears in this election campaign to have achieved something even Ed Miliband was unable to do: lose the majority support not only of Britain’s skilled workers, dubbed social class C2 by the pollsters, but also the DEs – the semi-skilled, unskilled and unemployed.

As the social class breakdown in Monday’s Guardian/ICM poll shows, the Conservatives enjoy an overwhelming 55% to 29% lead over Corbyn’s Labour party among the critical C2 voters.

This social group holds the key to many Midland and north-west marginal seats that have not seen a Conservative MP since Margaret Thatcher’s landslide victories of the 1980s. Indeed, polling data from the 1980s suggests that Thatcher, while capturing a significant proportion of the skilled working-class vote, never established a lead among them.

The latest polls show Corbyn has lost majority support even among the DEs. This week’s ICM figures report a Conservative lead with semi-skilled, unskilled and unemployed voters of 40% to 36%.

This is narrower than a week ago, which suggests the leaked launch of Labour’s manifesto may have helped Corbyn regain some ground. The sample sizes are small and a word of caution should be entered but it is still extraordinary that Labour does not have an opinion poll lead among this group of voters who must be considered at the heart of its historic core support.

This week’s Guardian/ICM poll confirms that the only groups Labour enjoys majority support with are 18- to 24-year-olds by 57% to 22%, non-white voters by a much narrower 40% to 38%, and students by a much more comfortable 65% to 16%.

All three groups have much lower turnouts than the rest of the voting public. The registration drive seems to have had some impact among students though, with those most certain to vote on 8 June rising from 45% to 52% in the past week.

Any signs of a Labour advance, however modest, in the headline voting intention figures is quickly disabused by a look at the polling data for the Labour marginals.

Voting intention figures in seats with a Labour majority of less than 15% in England and Wales – about 60 seats with majorities up to 7,000 – show a commanding Tory lead in this battleground.

A week ago ICM showed a 10-point Tory lead over Labour by 48% to 38% in these key marginals. That has now become a 20-point lead by 52% to 32%. The Tories’ sophisticated social media and marketing campaign aimed at Labour marginals appears to be making significant headway while Labour’s campaign appears to have a less sharply focused approach.

It is this battle in the Labour marginals that will determine the scale of May’s expected victory and it is these working-class voters who hold the key. That is why May is keen to stress her commitment to council housing and workers’ rights in a way that has not been seen in the Tory party since the 1970s.

Cameron could never claim with credibility, as May did on Monday, that “the Conservative party is the unashamed voice of ordinary working people once again”. The prime minister may not be promising to match Labour’s commitments to ban zero-hours contracts or raise the national minimum wage to £10 but her workers’ rights programme marks a decisive break from Thatcher’s “enemy within” attacks on the unions.

The polling data appears to show May has already won what could prove the early decisive rounds in this election campaign battle to be the workers’ party.