Health officials in Essex are looking for anyone who may have come into contact with a person infected with the Omicron variant of coronavirus.
The person who tested positive for Omicron visited a school, a church and a KFC restaurant.
Nine cases of the new COVID-19 variant had been identified in the UK as of Monday morning, one of which was in the Brentwood area of Essex.
On Monday, officials there said pupils and staff at a primary school are being tested, while visitors to a nearby KFC are also being urged to take a PCR test immediately.
Essex County Council said a number of other sites are being targeted for testing, including a church.
The person in Essex infected with the Omicron variant was said to be isolating with their family and not seriously ill or requiring hospitalisation.
Dr Mike Gogarty, Essex county council’s director of public health, said the infected person in Essex was indirectly linked to a traveller returned from South Africa two weeks ago, The Guardian reported.
Dr Gogarty told the BBC: “This case contracted the case from somebody else who contracted it from one of her family who had been recently to Africa.”
Three cases have been found in England: the one in Essex, another in Nottingham and a third in a person who had visited Westminster in London but who is no longer in the UK.
On Monday, Essex County Council said pupils and staff at Larchwood Primary School in Pilgrims Hatch, Brentwood, are being tested after a link was found with the new Omicron variant.
Trinity Church in Pilgrims Hatch is also the focus of targeted testing, the council said.
A joint statement from the council and the school said both were working with the UK Health and Security Agency and the Department of Health and Social Care to “take necessary precautionary action to prevent the spread”.
It said: “This includes making specialist testing available for all pupils and school staff and confirming arrangements for remote learning for one class.
"We appreciate that this is an unsettling time for parents, pupils and the school community but we take the time to remind everyone that this is a precautionary measure."
Essex County Council said the Brentwood case is linked to the other infection in Nottingham, with that individual understood to have arrived from southern Africa before coming into contact with the person in Essex.
Visitors to the KFC on Brentwood High Street between 1pm and 5pm on Friday 19 November are being urged to take a PCR test immediately.
Members of the congregation who visited Trinity Church in Pilgrims Hatch on 21 November were issued with the same call by Essex County Council.
They are being urged to attend mobile testing units, for drive-through appointments only.
Of the six Omicron variant cases identified in Scotland, four are in the Lanarkshire area and two in the Greater Glasgow and Clyde area.
Scotland’s deputy first minister, John Swinney, said some of the cases identified have no travel history, which suggests there is community transmission.
On Saturday, in response to the arrival of the Omicron variant in the UK, prime minister Boris Johnson announced that face masks will be made compulsory on public transport and in shops in England from Tuesday.
Watch: Boris Johnson announces new COVID measures after Omicron reaches UK