UK Prime Minister Boris Johnson ordered Britons on March 23 to stay at home to halt the spread of coronavirus.

These curbs are imposed on everyday life without precedent in peacetime.

Johnson said in a televised address to the nation that all but essential shops must close immediately and people should no longer meet family or friends or risk being fined.

"From this evening I must give the British people a very simple instruction — you must stay at home," Johnson said in a televised address, replacing his daily news conference.

People can only leave their homes to shop for basic necessities, exercise, for a medical need, to provide care or travelling to and from work where absolutely necessary.

Clothing stores, as well as other premises including libraries, playgrounds and outdoor gyms, and places of worship will be closed.

Johnson had resisted pressure to impose a full lockdown, but was forced to change tack as projections showed the health system could become overwhelmed.

Deaths from the virus in Britain jumped 54 to 335 on Monday.

"That's all — these are the only reasons you should leave your home," he said.

The new measures would be reviewed in three weeks, and relaxed if possible.

"These rules are not optional," London Mayor Sadiq Khan said.

The opposition Labour Party Leader Jeremy Corbyn said he supported the measures.

Police chiefs said the moves were sensible, and that they would be working with the government on how to enforce them.

The tougher tone followed evidence at the weekend that many were ignoring official guidelines.

People still avoided social distancing by going outdoors.

Under the new measures, the government will stop all gatherings of more than two people in public who do not live together.

It will also stop all social events​, including weddings and baptisms but not funerals.

The government said the military would help ship millions of items of personal protective equipment (PPE) including masks to healthcare workers who have complained of shortages.