Eight further cases of the Omicron variant have been confirmed in England, bringing the total number identified in the country to 13, the UK Health Security Agency (UKHSA) said.
Nine cases have also been identified in Scotland, meaning 22 cases have been identified across the two countries.
The UKHSA said confirmed cases have now been identified in the East Midlands, the East of England, London and North West.
Officials said that individuals who have tested positive and their contacts are all isolating.
Work is under way to identify any links to travel to southern Africa, the UKHSA said.
Dr Jenny Harries, chief executive of UKHSA, said: “We are continuing our efforts to understand the effect of this variant on transmissibility, severe disease, mortality, antibody response and vaccine efficacy.
“Vaccination is critical to help us bolster our defences against this new variant – please get your first, second, third or booster jab without delay.”
She added: “Following the change in JCVI advice yesterday, a booster dose for everyone over 18 years is now recommended at a minimum of three months from your last primary course jab.
“Please take up this offer as soon as you are invited to protect yourself, your families and your communities.
“Please make sure to wear a mask in line with Government guidance, including on public transport and in shops, to help break the chains of transmission and slow the spread of this new variant.
“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.
“That’s why it’s critical that anyone with Covid-19 symptoms isolates and gets a PCR test immediately.”
UKHSA said that there were now two cases in Barnet, one in Brentwood, two in Camden, one in Haringey, one in Liverpool, one in north Norfolk, one in Nottingham, one in Sutton, another in Wandsworth and two in Westminster.
The University of Nottingham confirmed that one of its students is among the the Omicron cases.
A university spokeswoman said: “Whilst we do not ordinarily comment on individual cases, we can confirm that a student is among the increasing number of people reporting cases of the Omicron variant nationwide.
“The student has been off campus and self-isolating throughout the period of infection. We are supporting them in liaison with the public health authorities and wish them a speedy recovery.”
The university currently has fewer than 20 Covid-19 cases among a total student population of 35,000, with all those affected self-isolating in line with national guidance.