Face masks compulsory in England from Tuesday
Health Secretary Sajid Javid has said face masks will be compulsory in shops and on public transport in England from Tuesday in response to the new Omicron variant.
It brings England in line with other parts of the UK. The PM also announced earlier that PCR tests would be required for all overseas arrivals.
Arrivals from 10 new red list countries will need to quarantine for 10 days.
MPs are due to vote on confirming the measures after they come into force.
The government has stopped short of extending vaccine passports in England and issuing advice to work from home, which are part of its Plan B - a contingency plan if intervention on Covid is needed to protect the NHS.
Mr Javid told Sky News the actions being taken were "proportionate and balanced", and he hoped they could be lifted "within weeks".
He told the Trevor Phillips on Sunday programme it would be "irresponsible" to make guarantees about Christmas, but said people should continue with their plans.
"I think it's going to be a great Christmas," he said.
The health secretary said tighter rules on testing for overseas arrivals would be implemented "as soon as possible" with the agreement of the UK's four nations.
But Mr Javid said the country was "nowhere near" reintroducing measures such as working from home or social distancing, arguing that they carry a "heavy price" economically, socially and in terms of mental health.
He added that he was expecting the government's vaccines advisers to advise him "imminently" on broadening the booster programme to younger age groups.
At a Downing Street news conference on Saturday, the prime minister called the new measures temporary and precautionary - and said they would be reviewed in three weeks, just before most schools break up for the Christmas holidays.
Labour has called for full implementation of Plan B and for improved sick pay to encourage self-isolation.
Boris Johnson announced the restrictions after it was confirmed that two Omicron cases had been detected in Brentwood, Essex, and Nottingham. Officials said the cases were linked and connected to travel in southern Africa, where the new variant was first identified.
Mr Johnson said: "We need to slow down the spread of this variant here in the UK, because measures at the border can only ever minimise and delay the arrival of a new variant rather than stop it all together."