The UK is grossly underestimating the incidence of Covid-19 and encouraging infected people back to work while ignoring key symptoms, a leading expert has claimed.

Professor Tim Spector, head of the department of genetic epidemiology and leader of the Covid symptom study app at King’s College London, said 50,000 to 70,000 people in the UK with Covid-19 are not being told to self-isolate.

He blamed Public Health England (PHE) and the wider tracking strategy, saying an insistence that only temperature and cough were the major symptoms was missing thousands of cases.

He told BBC Radio 4’s Today programme that 1.5 million people were logging onto the King’s app and tracking a wide range of symptoms and changes.

“It tells us that we’ve got at least 100,000 cases at the moment of people who are infected,” he said.

“And this is from our data, although the NHS would underestimate that because they’re not counting all the symptoms.”

He said the NHS was failing to track all symptoms of coronavirus, including loss of taste and smell.

“We list about 14 symptoms which we know are related to having a positive swab test, and these are not being picked up by the NHS.”

He said 17 other countries including the US had altered their list of symptoms, but not the UK.

“At the moment, people are being told to go back to work if they’re a care worker, and they’ve got something like loss of smell or taste or severe muscle pains or fatigue –  things that we know and we’ve shown are related to being swabbed positive,” he said.

“This country is missing the ball in underestimated cases but also putting people at risk, and continuing the epidemic.

“So we really do need to tell Public Health England to get in line with the rest of the world, and make people more aware.

“There’s no point telling people to be alert if they don’t know the symptoms.

“At the moment they’re not really being offered tests, and they’re being told not to self isolate if they don’t have the fever and the cough and it’s probably around half of the people in the population who are in that situation.

“We are probably missing at the moment between 50,000 and 70,000 people out there who are infected.

“We know that their swab tests will be positive.

“Someone has got to urgently ask this question of why we’re the only country in this crisis that isn’t really widening our group of symptoms and get on with it and do something.”