Guardian analysis indicates Labour is on course to lose Commons seats even in areas where it held on to councils

Theresa May would be in touching distance of a 100-seat Commons majority if this week’s local election results were repeated in the general election on 8 June, according to a Guardian analysis of voting patterns in key marginal seats.

The analysis shows that the swing to the Conservatives since the last comparable local elections would be sufficient to easily win Labour-held marginals such as North East Derbyshire, which is 18th in the Tory target list, Bridgend which is 20th, Wrexham (25th) and Gedling in Nottinghamshire (28th).

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But the detailed results show Labour seats to be vulnerable in areas where it held on to majority control of the council, such as Flintshire and Newport. In the two Labour marginals of Delyn (37th) and Alyn and Deeside (39th) in Flintshire, a repeat of Thursday’s 4% swing from Labour to Conservative would see Labour lose both seats despite holding on to the council.

This effect is even more pronounced in Newport. Jeremy Corbyn’s party took some comfort from the successful defence of the council but below the surface there was a 9% swing against Labour, which would be enough for the party to lose Newport East (43rd Tory target) and even Newport West (60th) which the Conservatives would take on a swing of 6.7% at the general election.

The analysis of council voting patterns in marginal seats shows that the swing to the Tories will not necessarily happen in a uniform way. While Labour would lose Gedling in Nottinghamshire because of 15-point swing from Ukip to the Conservatives, the Tories would fail to take Mansfield.

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The Labour vote held up in wards in both Nottinghamshire constituencies on Thursday but the difference was in what happened to the Ukip vote. In Gedling, it fell from 22% to 5%, nearly all of it going to the Conservatives, but in Mansfield it fell from 19% to a more resilient 10% which would leave Labour holding on to the seat.

The projection that May would be within touching distance of a 100-seat majority is born out by the BBC projected national vote share of 38% Conservatives (up three from 2015 local elections), Labour 27% (down two), Lib Dems 18% (up seven), Ukip 5% (down eight) and others on 12%. This implies a 2.5% swing from Labour to Conservative or a Commons majority of 56 compared with the 2015 local elections.

But in 2015 the Tories went on to poll even better at the subsequent general election, as happened in both of Margaret Thatcher’s landslide victories in 1983 and 1987. On the basis of this marginals analysis, May is heading for a majority of 80-100.

Prof Will Jennings of Southampton University and the Polling Observatorysaid the results confirmed that the Conservatives were looking at a sizeable victory on 8 June, but added it was still not possible to be sure of the scale. He said that, crucially, the results confirmed the national polling picture of the Conservatives enjoying an unassailable lead over Labour and steadily peeling off Ukip voters, while also making gains in Scotland.

“The big uncertainty is how turnout will affect the final margin,” he said. “Events like the mayoral loss in Tees Valley suggest Labour may be in for a harrowing night unless something dramatic happens during the remainder of the campaign.

“If there was any doubt, these results confirm that Corbyn’s leadership is steering Labour towards a bad defeat in the general election. Labour is weak everywhere – in Scotland, England and Wales. There are arguably no crumbs of comfort for it. A lack of enthusiasm leading to depressed levels of turnout surely must be a big danger for Labour on June 8.”