Most people who test positive for coronavirus do not have any key symptoms on the day of their test, a study has found.
The research showed that 77 per cent of people who had a positive test had no symptoms, the research showed.
Some 86 per cent did not have a cough, temperature or loss of taste/smell.
The study found that of the 115 (0.32 per cent) who had a positive test result, 27 (23.5 per cent) were symptomatic and 88 (76.5 per cent) were asymptomatic on the day of the test.
When looking at cough, fever and loss of taste/smell - seen as the three main symptoms - 86.1 per cent of those who tested positive had none of these.
Professor Irene Petersen at University College London (UCL) said people may have had symptoms in the days before their test or developed them later, but the figures suggested large numbers may be spreading the virus while asymptomatic.
She said: "They may be silent transmitters and they don't know about it. And so I think that's a problem.
"You may have a lot of people who are out in the society and they're not self-isolating because they didn't know that they are positive."
She said university students are one group who should be tested regularly, and definitely before they go home for Christmas.
"I think you could seed a lot of new infections around Christmas - you're indoors, you sit around the table," she said.
"Hopefully they can get that (testing) up and running before Christmas, I don't think they should wait until Christmas."
The researchers said there was a need to change testing strategies.
"Covid-19 symptoms are a poor marker of (Covid) infection," they wrote in the journal Clinical Epidemiology.
"In order to capture 'silent' transmission and potentially prevent future outbreaks, test programmes should involve frequent and widespread (Covid-19) testing of all individuals, not just symptomatic cases, at least in high-risk settings or specific locations."
Prof Petersen added: "Future testing programmes should involve frequent testing of a wider group of individuals, not just symptomatic cases, especially in high-risk settings or places where many people work or live close together such as meat factories or university halls."
A Department of Health and Social Care spokesman said: "Since the beginning of this pandemic we have prioritised testing for health and care workers to ensure all NHS staff have consistent access to testing.
"NHS staff with symptoms can access testing as a priority and staff in outbreak areas can access tests if they are asymptomatic. We will continue to expand testing availability as our capacity expands to 500,000 tests a day by the end of October."
The researchers analysed data from the Office for National Statistics (ONS) coronavirus infection survey, which has been testing thousands of households every week regardless of whether people have symptoms.
The analysis looked at data for 36,061 people who had a test between the end of April and the end of June.