LOCKDOWN is now in effect for Britain, with strict new measures imposed from this evening.

Prime Minister Boris Johnson has this evening ordered that people stay in their homes unless it is absolutely necessary that they go out.

The lockdown is expected to last for at least three weeks, at which point the measures will be reviewed.

People may only leave their home to shop for basic necessities, for medical needs, to travel to and from work and for one form of exercise a day, alone or with a family member you live with.

"To put it simply, if too many people become seriously unwell at any time, the NHS will be unable to handle it," Mr Johnson said.

"It is vital to slow the spread of the disease."

"The time has now come for us all to do more. We must stay at home, because the critical thing we must do is to stop the disease.

"That is why you will only be allowed to leave home for essential shopping, one form of excercise a day, any medical need or to provide care, and for travelling to and from work, but only if this is absolutely necessary."

The PM warned that people should not leave home to meet with friends or family they do not live with.

He urged people to use food delivery services where they can.

"The police will have the powers to enforce these rules," Mr Johnson said.

All shops selling non-essential goods, including electronic goods and clothing stores, will be closed with immediate effect, and all social gatherings will be stopped.

Parks will remain open for exercise, but gatherings will be dispersed.

Yesterday the PM warned that if people do not follow social distancing measures, the government will be forced to take further measures.

"We would need to look at the kind of measures other countries have been forced to bring in," Mr Johnson said in response to a question from a journalist.

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"I do not want to do that, and it is very important that the pleasure of being able to go out is preserved, but it can only be preserved if people act responsibly.

"If we cannot do that, then yes, we will have to bring forward further measures."

The government had previously announced measures to prevent social gatherings, including ordering pubs, restaurants and schools to close.