Scientists and medical experts have accused the British government of ignoring what they say could be the most damaging consequence of removing almost all pandemic restrictions from July 19 — increasing the number of people affected by debilitating “long Covid” that can last for months or years.

“Many of us have been urging the new health secretary Sajid Javid to consider long Covid when evaluating the easing of lockdown,” said David Strain, a senior clinical lecturer and Covid researcher at Exeter University.

“But he does not seem to have taken it into account at all, even though long Covid is probably going to have more impact on the economy than any other aspect of the pandemic,” he added.

Estimates of the proportion of people with Covid after-effects differ, but most experts put the figure at 10 to 20 per cent of those who remain out of hospital and about 90 per cent in hospitalised patients.

Common symptoms include fatigue, breathing problems, insomnia and “brain fog”, leaving many sufferers unable to work.

“I am baffled that Javid could throw out figures like 100,000 new cases a day without mentioning the number who might develop long Covid,” said Nathalie MacDermott, clinical lecturer at King’s College London. “That could leave an enormous legacy of more than 10,000 cases a day of long Covid.”

Although vaccination has weakened the links between Sars-Cov-2 infection, hospitalisation and death, scientists do not know the extent to which it has reduced the risk of suffering long-lasting symptoms.

Long Covid was highlighted in a letter published by The Lancet on Wednesday night by 122 scientists and doctors from the UK and overseas, calling on the government to rethink its “dangerous and premature” reopening plans.

The letter warned that following the lifting of lockdown restrictions later this month, “exponential growth [in Covid cases] will probably continue until millions more people are infected, leaving hundreds of thousands with long-term illness and disability”.

“This strategy risks creating a generation left with chronic health problems and disability, the personal and economic impacts of which might be felt for decades to come,” wrote the signatories.

Scientists said that although Javid and Boris Johnson, the prime minister, hardly mentioned long Covid in their statements on unlocking this week, the government’s chief medical adviser, Chris Whitty, did issue a warning when he spoke to the Local Government Association annual meeting on Tuesday.

“Since . . . [infection] rates are going up, I regret to say I think we will get a significant amount more long Covid, particularly in the younger ages where the vaccination rates are currently much lower,” Whitty said.

“The deaths from Covid . . . are mercifully going to be much lower in this wave compared to the previous ones as a proportion of cases but long Covid remains, I think, a worry,” Whitty said, adding: “We don’t know how big an issue it’s going to be but I think we should assume it’s not going to be trivial.”

Children and teenagers are less likely to be affected by long-lasting coronavirus symptoms than older people, said Janet Scott, clinical lecturer in infectious diseases at the University of Glasgow, but they are not immune.

Scott was part of an international team that studied 500 children who were admitted to hospital with Covid-19 in Moscow last year. A quarter had persistent symptoms six months after discharge.