British Prime Minister Boris Johnson first eased England's lockdown on June 1, and has since re-opened more of the economy.

The research showed the rates of infection fell during May, the last month of full lockdown, halving every eight to nine days.

The study - which is a "pre-print", meaning it has yet to be peer-reviewed - found there were on average 13 positive cases for every 10,000 people, with an overall reproduction number of 0.57.

That is lower than the government's official figures for that time, estimating a so-called "R" number of 0.7-0.9 when lockdown was eased. An R number of less than 1 indicates an epidemic is shrinking.

"Our level of adherence in the UK, and the overall average behavior was very effective at reducing transmission of the virus," Steven Riley, Professor of Infectious Disease Dynamics, Imperial College London, told reporters.

Over 120,000 volunteers were tested as part of the study, which health minister Matt Hancock said showed the government took the "right actions at the right time".

The research also found that young adults were more likely to test positive than other age groups, indicating the need for them to follow social distancing even if their symptoms are often less severe than for older people.

It also said that people of Asian ethnicity were more likely to test positive, which might account for higher death rates in that group.

A separate pre-print study of a pilot test-and-trace scheme on the Isle of Wight found that it had reduced total incidence of infections and the R number faster than in other areas of the UK.