The UK must maintain some form of social distancing until a coronavirus vaccine is found, a scientist advising the government has said.
Prof Neil Ferguson told the BBC there was “little leeway” to relax measures without “something… in their place” – such as testing and contact-tracing.
A three-week extension to the lockdown is expected to be announced later.
Labour said it would support an extension, but called for details on how and when the lockdown will end.
Prime Minister Boris Johnson introduced strict curbs on life in the UK on 23 March, as the government sought to limit the spread of the virus.
Ministers are required by law to assess whether the rules are working, based on expert advice, every three weeks.
The government – led by Foreign Secretary Dominic Raab as Mr Johnson continues to recover from the virus – will detail the outcome of the first assessment at the daily Downing Street news conference later.