David Frost has branded Covid lockdowns a “serious mistake”, stepping up his criticism of the beleaguered Boris Johnson as he fights to stay in office.

       The former Brexit minister – who resigned last month – said there were too few voices “challenging the epidemiologists”, calling mask-wearing and Covid passes “stuff that doesn’t work”.

       Lord Frost also criticised the drive to achieve ‘net zero’ carbon emissions, saying: “We are rushing at some of this stuff. We’re bringing in measures that are sort of unnecessary, too soon.”

       The criticisms confirm the former close Johnson ally is now firmly aligned with backbench MPs determined to end all Covid rules and who believe he is “not Tory enough”.

       On lockdowns, Lord Frost said: “I think, honestly, people are going to look back at the last couple of years globally and see lockdown as a pretty serious public policy mistake.

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       “I would like to see the government ruling out lockdowns for the future, repealing the legislation, ending them. We can’t afford it, it doesn’t work,” he told a Daily Telegraph podcast.

       “Stop doing Covid theatre – vaccine passports, masks, stuff that doesn’t work – and focus on stuff that does work. Stuff like ventilation, antivirals, proper hospital capacity – that’s what we need to be focussing on.”

       On the climate emergency, Lord Frost criticised “technologies that aren’t ripe, trying to pick winners, trying to subsidise technologies that may not be the best way forward”, saying: “That is increasing costs on individuals.”

       Many suspected Lord Frost resigned because Mr Johnson forced him to soften his hardline stance on the Northern Ireland Protocol, in his deadlocked talks with the EU.

       But he insisted it was Covid policy, saying: “That was the reason I resigned, that’s what took me out of the government.

       “I didn’t agree with the plan B measures, masks, vaccine passports – that’s what forced me out.”

       The government is widely expected to lift plan B after a review in two weeks’ time, or possibly earlier, as Omicron cases peak at a level lower than feared before Christmas.

       The prime minister stepped back from imposing tougher restrictions after a cabinet revolt and to avoid another damaging Commons clash with his own MPs.

       His future hangs in the balance after his dramatic Commons confession that he did attend a No 10 garden party – while claiming he did not realise it was a party.

       Tory MPs say his fate is now in the hands of Sue Gray, the Cabinet Office civil servant investigating the controversy, although it is unclear whether she will judge whether rules were broken.

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       Some senior Conservatives – Scottish leader Douglas Ross, rising star William Wragg and ex-minister Caroline Nokes – have called for him to quit immediately.

       Amid the crisis, Tory poll ratings continue to plunge to 28 per cent in one survey – while the chancellor Rishi Sunak has refused to back the prime minister before the inquiry has concluded.