Watch: COVID-19: UK calls meeting of G7 health ministers to discuss Omicron variant as third case found in Britain
The UK has called an "urgent" meeting of G7 health ministers on Monday to discuss the Omicron COVID variant - after a third infected person was found in Britain.
The individual, who is no longer in the country, tested positive after travelling here and "is linked to travel to southern Africa".
The UK Health Security Agency (UKHSA) is now carrying out targeted testing in places the person visited when they were likely to be infectious - including, it is thought, Westminster.
In another development on Sunday evening, it was announced that all those arriving in the UK from 4am on Tuesday will be required to take a PCR test on or before day two.
They must "self isolate until they have received a negative test result", the Department of Health and Social Care (DHSC) said.
Tests must be purchased from private providers, and "free NHS tests are not valid for this purpose", the department added.
Also from 4am on Tuesday, face coverings will be compulsory in shops, banks, post offices, hairdressers and on public transport in England, except for those who are exempt.
Regarding Monday's gathering of ministers, the DHSC said: "Under the UK presidency an urgent meeting of G7 health ministers will be convened on Monday 29 November to discuss the developments on Omicron."
Watch: Omicron symptoms: What are they, and how do they compare to other COVID infections?
Discussing the new mutation, Dr Jenny Harries, UKHSA chief executive, said: "Our advanced sequencing capabilities enable us to find variants and take rapid action to limit onward spread.
"It is very likely that we will find more cases over the coming days as we are seeing in other countries globally and as we increase case detection through focused contact tracing."
She said UK officials are continuing their efforts to understand the effect of the variant on transmissibility, severe disease, mortality, antibody response and vaccine efficacy.
"It's critical that anyone with COVID-19 symptoms isolates and gets a PCR test immediately," she said.
"Vaccination is critical to help us bolster our defences against this new variant - please get your first, second or booster jab without delay."
She urged people to wear a mask in crowded places, including public transport and shops, "to ensure we all help break the chains of transmission and slow the spread of this new variant".
Sajid Javid said there would also be targeted testing in the areas where the first two cases were found - Brentwood in Essex, and in Nottingham.
The two individuals are self-isolating along with their households while further tests were carried out, he added.
The two cases were "linked", the health secretary said, and that connection has been traced to South Africa.
The variant has prompted the UK to place ten African countries on the red list - South Africa, Namibia, Lesotho, Botswana, Eswatini, Zimbabwe, Angola, Mozambique, Malawi and Zambia.