A coronavirus “variant of concern” first detected in Brazil has now been found in the UK.
Three cases have been detected in England and separately three in Scotland.
In England, officials are still trying to track down one of those who tested positive for the new variant.
The three Scottish residents had flown to north-east Scotland from Brazil via Paris and London, the Scottish government said.
Experts believe this variant (P1) – first detected in travellers to Japan from Manaus in northern Brazil in January – could be more contagious.
There are also concerns vaccines may not be as effective against it – but NHS England’s Prof Stephen Powis said vaccines could be “rapidly adapted”.
Dr Susan Hopkins, from Public Health England (PHE), said the UK was more advanced than many other countries in identifying the variants and mutations and therefore able to act quickly.
In England, the first two cases are from the same household in South Gloucestershire after someone returned from Brazil on 10 February – five days before the government’s hotel quarantine rule came into force.
Two other people in the same household have also since tested positive for Covid – but tests are still ongoing to check if it is the same variant, so they are not included in the overall UK total of six.
PHE said officials are now tracking down passengers who were on the same flight from Sao Paulo to Heathrow, via Zurich.
The third case identified in England is not linked to the other two cases and the whereabouts of that person are still not known.
PHE said the person did not complete their test registration card so follow-up details are unavailable.
Officials are asking anyone who took a test on 12 or 13 February and who has not received a result or has an uncompleted test registration card to come forward immediately by calling 119.