UK residents have been urged to stop all non-essential contact as Prime Minister Boris Johnson warned them the country is heading for the “fast growth” part of the virus outbreak.
He asked people to work from home if they can, to not go to restaurants or the theatre, and to avoid unnecessary journeys.
The government will also stop “supporting” large gatherings usually attended by emergency workers such as the police or paramedics.
Mr Johnson warned Londoners to be particularly careful because the UK capital is “a few weeks ahead” of other places in the country.
Schools will not be closed chief scientific adviser Sir Patrick Vallance said the move remained under consideration.
“Now is the time for everyone to stop non-essential contact with others and to stop all unnecessary travel,” Mr Johnson said.
“We need people to start working from home where they possibly can.
“It looks as though we are now approaching the fast growth part of the upward curve and without drastic action cases could double every five or six days,” Mr Johnson said.
The Prime Minister said it was very strong advice but admitted it was not legally binding on people or institutions.
“By this coming weekend it will be necessary to go further and to ensure that those with the most serious health conditions are largely shielded from social contact for around 12 weeks,” Mr Johnson said.
He has been criticised by some for his comparatively lenient measures introduced in comparison to other countries in Europe who have ordered an effective lockdown in movement.
“We’re also recommending increased social distancing. That’s the phrase that you hear. Which means trying to reduce contact between people again to try to delay this transmission,” Sir Patrick said.
“That means where businesses can do it and where individuals can do it, home working is recommended. Unnecessary travel should be reduced and stopped.”
The government had appealed to some of its biggest industrial firms, such as Rolls-Royce, for help in manufacturing health equipment including ventilators as the coronavirus tightened its grip on the country.
Contingency plans to commandeer resources for the outbreak are gradually being put in place. Hotels will be used as makeshift hospitals, retired doctors are being asked to come back to work and some elective surgery is being cancelled.