Prime Minister Boris Johnson on Sunday admitted he was “too fat” when he contracted the coronavirus in March and exhorted Britons to use the restrictions imposed by the pandemic to lose weight, as new cases continued to surge across the UK.

The pandemic should be a “teachable moment” for the country, Johnson told the BBC’s Andrew Marr Show ahead of the Conservative party’s annual conference, being held virtually this year.

The UK recorded the highest daily rise of cases at 12,872 and 49 deaths by Saturday evening, but officials said a technical issue was responsible, having included infections not recorded earlier for the September 24-October 1 period.

The opposition Labour kept up pressure on the government’s handling of the pandemic. Party leader Keir Starmer said: “I think they’ve lost control of the virus. And I don’t want to see death rates go up. Nobody does. But this is serial incompetence.”

In the BBC interview, Johnson, who recovered from the virus after three days on the ventilator, dismissed as “drivel” claims that he was still suffering from the effects of coronavirus, known as “long Covid”.

“It is balderdash and nonsense. I can tell you I’m fitter than several butchers’ dogs.”

His government, Johnson said, was trying to achieve a balance between saving lives and protecting the economy, but cautioned that daily life would not return to normal until Christmas, perhaps even beyond.

He said: “On the one hand we have the imperative to save life, it is a moral imperative to save life if we possibly can. On the other hand we have to keep our economy moving and our society going. That is the balance that we are trying to strike”.

“If you ask me ‘do I think things can be significantly different by Christmas?’ Yes I do, and we’re working flat-out to achieve that. But be in no doubt that it is still very possible that there are bumpy, bumpy months ahead. This could be a very tough winter for all of us – we’ve got to face that fact”, he added.

Alex Norris, shadow health minister, criticised the interview: “Boris Johnson had the chance to map out a serious strategy to improve public confidence in the government’s handling of this crisis. Instead he waffled and ducked every question. His serial incompetence is holding Britain back”.