Britain is unlikely to lift its stringent lockdown rules until the end of May, once the spread of the coronavirus has started to slow, a leading government adviser said on Saturday as the death toll rose to 4,313.

The government has put Britain into a widespread shutdown, closing pubs, restaurants and nearly all shops, while ordering people to stay home unless absolutely essential to venture out.

The order is designed to curb the spread of COVID-19 in the country, which has almost 42,000 confirmed cases. But some experts have started to question whether the shuttering of the economy will cost more lives in the long run.

"We want to move to a situation where at least by the end of May we're able to substitute some less intensive measures, more based on technology and testing, for the complete lockdown we have now," Neil Ferguson, a professor of mathematical biology at Imperial College London, told BBC Radio.

Britain's death toll from the coronavirus rose by 20% to 4,313 by Friday afternoon with 708 new fatalities recorded, the health ministry said. That compared to a 23% rise on Thursday.

The peak of new cases could come within a week or 10 days, Ferguson said, but adherence to the strict rules will determine how quickly the rate of infections decline after that.