New government measures to help people shed weight include banning TV and online adverts for junk food before 9.00 p.m., ending "buy one get one free" deals on such foods, and flagging calories on menus of large restaurants plus possibly on alcohol.

Johnson, 56, who has lost more than a stone (6 kg) since a life-threatening brush with COVID-19, was responding to research showing that those who are obese or overweight are at increased risk of death or severe illness from the disease.

The prime minister has a reputation as a bon viveur, who in the past has spoken of enjoying an expensive bottle of red wine and late-night binges on chorizo and cheese. But he has also championed cycling to work and introduced so-called "Boris bikes" in London for public use when mayor of the capital.

Last month, Johnson said British people were fatter than most European counterparts apart from Malta and his government targeted "tackling the obesity time bomb".

"I was too fat"

"I've always wanted to lose weight for ages and ages and like many people I struggle with my weight, I go up and down. But since I recovered from coronavirus I have been steadily building up my fitness," he said in a Twitter video on Monday.

"When I went into ICU [intensive care] when I was really ill, I was way overweight ... and, you know, I was too fat," he added, describing his new regime as a gentle run in the morning which gives him more energy during the day.

Johnson, who has often mocked state "nannying", said he hoped the new health campaign was not "excessively bossy" but rather a gentle nudge for Britain to get fitter.

With more than 60% of adults in Britain considered overweight or obese, according to Public Health England, a "Better Health" campaign will be introduced with weight management services expanded in the National Health Service.

The opposition Labor Party said it had heard "big promises" from the ruling Conservatives before and criticized them for past health service cuts.

"An effective obesity strategy needs action, not consultation," said Labor’s health and social care policy chief Alex Norris. "The Tories [Conservatives] have pared public health to the bone and people are paying the price for ten years of this complacency."