Almost 60% of patients who were subsequently confirmed as positive for COVID-19 had reported losing their sense of smell and taste, the data analysed by the researchers showed.

That compared with 18% of those who tested negative.

These results, which were posted online but not peer-reviewed, were much stronger in predicting a positive COVID-19 diagnosis than self-reported fever, the researchers at King's College London said.

Of 1.5 million app users between March 24 and March 29, 26% reported one or more symptoms through the app. Of these, 1,702 also reported having been tested for COVID-19, with 579 positive results and 1,123 negative results.

Using all the data collected, the research team developed a mathematical model to identify which combination of symptoms - ranging from loss of smell and taste, to fever, persistent cough, fatigue, diarrhoea, abdominal pain and loss of appetite -was most accurate in predicting COVID-19 infection.

"When combined with other symptoms, people with loss of smell and taste appear to be three times more likely to have contracted COVID-19 according to our data, and should therefore self-isolate for seven days to reduce the spread of the disease," said Tim Spector, a King's professor who led the study.

Spector's team applied their findings to the more than 400,000 people reporting symptoms via the app who had not yet had a COVID-19 test, and found that almost 13% of them are likely to be infected.

This would suggest that some 50,000 people in Britain may have as yet unconfirmed COVID-19 infections, Spector said.

Official figures showed confirmed cases rose 14% in Britain between Monday and Tuesday to 25,150 as of Tuesday at 0800 GMT. The government said 1,789 people have died in hospitals from coronavirus as of 1600 GMT on Monday.