Boris Johnson’s approval rating has slumped in the wake of Dominic Cummings’ explosive evidence about the government’s handling of the coronavirus pandemic, an opinion poll suggests.

According to the Opinium study, the prime minister’s approval rating now stands at -6% -compared with +6% two weeks ago.

But it seems that Labour leader Sir Keir Starmer has not benefited from the shift in public opinion. His net approval rating is at -9%, which is the same as a fortnight ago.

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Five key moments from Cummings’s testimony

The poll now puts the Conservatives on 42%, down two points since the last poll. Meanwhile, Labour is on 36% after gaining five points.

Only one in five of those polled said they trusted Dominic Cummings to tell the truth – however, the research suggests that many of the claims he made during seven hours of testimony to MPs were believed.

While 66% of respondents said they believed the former senior adviser’s claim that the government pursued a herd immunity strategy at the start of the pandemic, 20% said they believed this was false.

Separately, 60% said they believed the allegation that Mr Johnson thought coronavirus was a “scare story” and called it “the new swine flu”, with 24% saying that was false.

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When it comes to Matt Hancock, 44% think that the health secretary should resign, compared with 30% who think he should stay.

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Opinium’s head of political polling Adam Drummond said: “Whilst Dominic Cummings is seen as one of the least trustworthy men in Britain, the public do see some truth in the allegations he made against Boris Johnson’s government, puncturing the Conservatives’ post-Hartlepool bounce and reversing a recent spike in the prime minister’s approval rating.

“However, there are strong reasons to believe that this won’t last though as the underlying approval figures for the vaccine rollout, which has driven voting intention since the beginning of 2021, are unchanged and remain very strong.”

A total of 2,004 UK adults were polled from 27 to 28 May.