Today shadow health secretary Jonathan Ashworth is writing to Hancock to demand answers, amid fury from campaigners and officials, who point out that it is less than a month since Boris Johnson, the prime minister, launched a national anti-obesity strategy, claiming it was crucial to the fight against Covid-19 and the nation’s health.

But last week Hancock pulled the plug on Public Health England, the body that has been responsible for fighting obesity, and announced that it would be replaced by the National Institute for Health Protection that would focus on external threats to the UK, pandemics and infectious diseases, but not inherit the public health protection roles of PHE.

The move followed weeks of speculation that ministers, including Johnson, were unhappy with PHE’s performance over the testing of coronavirus swab samples and tracing of people suspected of being infected, especially early in the pandemic.

However, doctors, hospital bosses and health experts said it was an unnecessary and high-risk move aimed at distracting from the government’s own Covid-19 failings.

Ministers also announced that the immediate shake-up was going ahead even though they did not know who will take over PHE’s work in tackling obesity, reducing smoking and tackling health inequalities.

Writing in the Daily Telegraph at the end of July, Hancock said: “If everyone who is overweight lost five pounds, it could save the NHS over £100 million over the next five years.

“And more importantly, given the link between obesity and coronavirus, losing weight could be lifesaving.”

Today Ashworth is asking Hancock to urgently explain who will now be responsible for obesity, drug and alcohol services, vaccinations, anti smoking, and sexual health services.

Ashworth told the Observer: “Not only is a major structural reorganisation mid-pandemic risky and irresponsible but it has left open big questions as to who will lead on important lifesaving health improvement agendas including obesity, anti-smoking, addiction and sexual health services. Weeks ago, Boris Johnson was telling us his obesity strategy was vital to building resilience ahead of a second wave. Now he can’t even explain who is responsible for delivering it.”

Gabriel Scally, visiting professor of public health at Bristol University and ex-NHS regional director of public health for the south-west, said: “There is a complete lack of clarity on what it is to happen to all the other functions currently carried out by Public Health England, whether it be other infectious diseases like tuberculosis and sexual transmitted diseases, or the really major non-communicable disease problems like obesity and tobacco.

That’s deeply worrying – but inevitable, given the chaotic way in which this decision was made and announced. It is the most incoherent and potentially damaging decision around public health structures in more than 150 years of public health in the UK.”

As for obesity, he added: “I never had any belief in the ability or desire of the government to do anything about it. It’s entirely naive to believe that they would. I don’t believe there’s any commitment [by this government] on any public health issue, obesity or anything else. It’s just not on their agenda. They are interested in private wealth, not public health.”

Tam Fry, chairman of the National Obesity Forum, said he had long doubted that successive governments were sufficiently committed to tackling obesity and that the latest decision by Hancock merely reinforced his scepticism. “Obesity is a national problem and only central government can take the many measures required to scotch it” he said.

Fry added that the long established target to cut obesity to levels registered in 2000 by the end of 2020 “hasn’t the faintest chance of being met” while Johnson’s pledge to cut childhood obesity by 50% by 2030 now “is probably pie in the sky without urgent draconian action”.

Maggi Morris, a former director of public health for Preston and Central Lancashire, who recently carried out a review of the research on the link between obesity and Covid-19, said: “It’s alarming because it’s yet another example of the collateral damage caused by the woeful management of Covid in this country. It’s yet more mayhem.” She added: “They’ve tried to look for a scapegoat in Public Health England.”

Whitehall sources said the government remained totally committed to the anti-obesity drive, and would be consulting widely about how best to take forward this work. The government’s strategy, announced on 27 July, included a crackdown on the promotion of high fat foods in shops and a 9pm watershed on junk food advertisements on television.