Live updates: follow the latest news on Covid-19 variant Omicron
Britain raised its Covid alert level on Sunday in response to the rapid spread of the Omicron variant as new rules to tackle the outbreak take effect.
Double-vaccinated people in England will have to take daily Covid tests from Tuesday rather than self-isolating in a renewed effort to slow the spread of the Omicron mutation.
On Monday the inoculation booster campaign is widened to include the over-30s and a senior doctor advised people to limit social interaction.
The Omicron variant is spreading through the UK and could cause 75,000 more deaths in England unless tougher restrictions are brought in, the London School of Hygiene and Tropical Medicine warned.
The chief medical officers of England, Scotland, Wales and Northern Ireland recommended an increase to alert level 4 from level 3 on its 5-point scale, which means they judge transmission of the virus to be high.
"Early evidence shows that Omicron is spreading much faster than Delta and that vaccine protection against symptomatic disease from Omicron is reduced," the medical officers said.
Daily testing rules come into effect on Tuesday and aims to reduce the stress on people identified as Covid contacts who, previously, would have had to self-isolate, the Department of Health & Social Care said.
Daily lateral flow tests will also help work out how and where the virus is spreading.
Close contacts of people who test positive are at higher risk of getting Covid-19 and one in three people show no symptoms.
The DHSC said the daily testing would help to ensure people were not unknowingly passing the virus on to others.
People contacted by the NHS Test and Trace system will be advised to ask for a box of seven lateral flow tests from a pharmacy, school or home delivery.
“The Omicron variant is quickly gaining ground in the UK and is expected to become the dominant strain by mid-December,” Health Secretary Sajid Javid said.
“We are taking this proportionate and more practical measure to limit the impact on people's day-to-day lives while helping to reduce the spread of Omicron. Vaccines remain our best defence.”
Unvaccinated adults are not eligible for the new daily testing policy and must continue to self-isolate for 10 days if they are a contact of someone who tests positive.
On Monday, everyone in the 30-39 age group will be able to have a booster, with appointments timed for three months after their second injection.
‘The most recent data shows boosters are the essential defence against Omicron and we are doing everything in our power to get jabs into arms as quickly as possible,” said Mr Javid.
People should minimise social contacts if they want to avoid catching Covid-19 and missing out on Christmas with their family, said Dr Susan Hopkins, chief medical adviser for the UK Health Security Agency.
“It transmits when we're with other people. And therefore when we are coming up to a time where we will have engagements that we want to make, family that we want to see, then ensuring that we have less contacts before those is important so that we don't transmit to others,” she said.
She also suggested taking lateral flow tests before going to social events.