Watch: PM announces tightening of coronavirus rules
Boris Johnson was joined by chief medical officer Professor Chris Whitty and Sir Patrick Vallance, the chief scientific adviser, for a Downing Street press conference on Saturday following the emergence of the Omicron coronavirus variant in the UK.
Here are the eight main things we learned from the press briefing:
1. Face masks will be compulsory in shops and on public transport in England from next week.
2. Anyone entering the UK from any destination abroad will have to take a PCR test two days after arrival and self-isolate until they have a negative result.
3. Anyone who has been in close contact with a case of Omicron will have to self-isolate for 10 days, regardless of their vaccination status.
4. The new measures will be reviewed within three weeks.
5. The two cases discovered in the UK were part of the same outbreak and are in Essex and Nottingham.
Watch: England 'nowhere near' introducing tougher Covid restrictions
6. Omicron can be spread between people who are double vaccinated.
7. The variant has an “extensive” mutation which means in may “at least in part” reduce the protection of the vaccine over time, the PM said.
8. Omicron “really changes the risk/benefit calculations” for the Joint Committee on Vaccination and Immunisation regarding recommending vaccines to younger children, meaning children under 12 could soon be eligible.