"Drastic" plans to respond to the coronavirus pandemic have been set out by the Government.
Here are some questions answered from the Downing Street briefing on coronavirus.
Who will this affect?
Most people in society have been asked to change their day-to-day lives in some way. It will particularly affect people over the age of 70, pregnant women and people with certain health conditions.
What will it mean for the general population?
Boris Johnson said: "Now is the time for everyone to stop non-essential contact with others and to stop all unnecessary travel."
The Prime Minister urged people to stay away from pubs, clubs, theatres and "other such social venues".
Where possible, people should work from home. He added that mass gatherings would no longer be supported by emergency workers.
What is 'whole household isolation'?
If one person in a house has symptoms, including a continuous cough or fever, the whole family should stay at home for 14 days.
They should avoid even going to the shops to get essentials, the Prime Minister said. People should only go out for exercise and ensure they do not come into contact with people while doing so.
What does it mean for vulnerable people?
In coming days, everyone classed as vulnerable will be asked to ensure they are "largely shielded from social contact" for around 12 weeks, or possibly longer. This includes people over the age of 70, pregnant women and people with certain health conditions.
Which illnesses will this include?
Advice has not yet been issued on exactly which illnesses this will include, but England's chief medical officer Professor Chris Whitty said "people who in adult life would normally be advised to have the flu vaccination" could be included.
This could include people with chronic diseases such as chronic heart disease or chronic kidney disease, he added.
What did the Prime Minister say about healthy older people?
"Many people, including millions of fit and active people over 70, may feel that there is something excessive about these measures, but I have to say that I believe they are overwhelmingly worth it to slow the spread of the disease, reduce the peak, to save life, minimise suffering and give our NHS the chance to cope," Mr Johnson said.
Why pregnant women?
Prof Whitty said that including pregnant women in this group was a "precautionary measure" as experts are "early in our understanding of this virus".
Is any part of the country worst affected?
The Prime Minister said the peak of the epidemic is coming faster in some parts of the country than others. "It looks as though London is a few weeks ahead," he said.
Are schools staying open?
Schools remain open at the moment. The Government's chief scientific adviser Sir Patrick Vallance said other measures may be necessary - including school closures - at some point.
"Those things need to be done at the right time," he said.
How long will this go on for?
Prof Whitty said measures to tackle the spread of the disease would need to be in place for a "prolonged period".
"This is going to go on for some time," he said. "We should not be under any illusions that 'if we just do this for a couple of weeks that is sufficient'."