This is a “moment of national emergency,” Boris Johnson told the British people this evening.

“I will give the British people a very simple instruction,” Johnson said in an address to the nation filmed in 10 Downing Street. “You must stay at home.”

People can only leave their homes for “very limited purposes.”

These include shopping for basic necessities, one form of exercise a day (alone or with a member of the household), a trip for “any medical need” and only essential travel to or from work.

“If you don’t follow the rules,” he added, “the police will have the power to enforce them.”

All shops selling non-essential goods will close. Libraries, playgrounds, outdoor gyms and places of worship will close too.

All gatherings of more than two people in public are banned, although parks will remain open for exercise.

All social events are banned including weddings and baptisms. Funerals will be allowed to continue.

“It is vital to slow the spread of the disease,” Johnson said. “There are just no easy options.”

The measures are “under constant review” and will be reviewed in three weeks.

The lockdown will allow the NHS more time to prepare for peak of the epidemic, the Prime Minister said. The government is in the process of buying millions of testing kits.

“I want to thank everyone who is working flat out to beat the virus,” he said. “Everyone from the supermarket staff, to the transport workers, to the carers, to the nurses and doctors on the front line.”

“Many lives will sadly be lost,” he concluded, but “there is a clear way through.” “We will beat the coronavirus and we will beat it together.”

The British government has come under huge pressure over the past week to enforce “social distancing” restrictions. It appears that the argument for lockdown was given greater moral force over the weekend. Members of the public continued to congregate in parks and markets.

It may be too late – measures taken now can only mitigate the spread of the disease in the near future.

There is little doubt that the address Johnson made tonight is the most serious in tone and content since the Second World War and it represents a near unprecedented expansion of the power of the British state, for there is no precedent for the circumstances we face.

We are not at war. In wartime, all able-bodied men and women direct their energies and drive towards the goals of the state and their lives are expended in the effort.

In the struggle with coronavirus it is different. It is overwhelmingly the frail and the old who are likely to die.