Everyone should avoid gatherings and crowded places, such as pubs, clubs and theaters
Everyone should work from home if they can
All "unnecessary" visits to friends and relatives in care homes should cease
People should only use the NHS "where we really need to" - and can reduce the burden on workers by getting advice on the NHS website where possible
By next weekend, those with the most serious health conditions must be "largely shielded from social contact for around 12 weeks"
The UK is now "three weeks" behind Italy - the worst-hit country in Europe
If one person in any household has a persistent cough or fever, everyone living there must stay at home for 14 days
Those people should, if possible, avoid leaving the house "even to buy food or essentials" - but they may leave the house "for exercise and, in that case, at a safe distance from others"
Schools will not be closed for the moment
Chief medical adviser Prof Chris Whitty said the group of people who should take "particular care to minimize their social contact" were:
People over the age of 70
Other adults who would normally be advised to have the flu vaccine (such as those with chronic diseases)
Mr Johnson said "drastic action" was needed as the UK approaches "the fast growth part of the upward curve" in the number of cases. He told Londoners to pay special attention to the advice as the virus is spreading more rapidly in the capital than elsewhere.
Health Secretary Matt Hancock told the House of Commons the number of people to have died with the virus in England had risen to 71 - and "the disease is now accelerating".
The first death in Wales, and a death in Scotland, brings the total number of deaths in the UK to 55.
Why has the UK plan ramped up?
The UK's plan has shifted because the scientific modelling showed we were on course for a "catastrophic epidemic".
A strategy of just slowing the spread of the virus, but not trying to stop it, would have overwhelmed intensive care units.