The British government said on Wednesday it would expand its COVID-19 national testing study, with an aim of reaching 400,000 people to provide weekly data on the spread of the infection and better locate future local outbreaks.

The Department of Health and Social Care said in a statement on Wednesday that it would initially test 150,000 people in England per fortnight by October, up from 28,000 people now.

The testing survey, undertaken by the Office for National Statistics, will also be extended to Scotland, Wales and Northern Ireland, aiming to eventually reach 400,000 across the United Kingdom.

Health minister Matt Hancock said the survey would help plug the gap in their knowledge of finding which people had the virus but were asymptomatic.

"Getting people who are asymptomatic to get a test is obviously challenging because often they don't know that they've got the virus but this survey will help us to pinpoint where the virus is even amongst people who don't know they've got it," he told BBC TV.

The government hopes the survey will provide a better national picture of the prevalence of the virus as well as allowing the authorities to narrow down which areas might be suffering local outbreaks, so fewer people would need to be affected by any local restrictions to curb the spread.