The outbreak of the Covid-19 variant in south London appears to have been triggered by an individual who travelled from Africa in February, it been reported by the BBC.
Surge testing has begun in Wandsworth and Lambeth after 44 confirmed and 30 probable cases were identified.
The country involved was not on the red list for mandatory hotel quarantine at that time, but it is now.
The prime minister’s official spokesman added that the cluster of cases of the South African variant was being taken “very seriously” and the “testing processes that we have in place have been working well”.
The link has not been proved beyond doubt, but is the working assumption of contact tracers.
According to the BBC an executive summary of the outbreak published on 12 April at 15:00 BST and marked “Official Sensitive” said the individual did self-isolate and requested a home test after showing symptoms.
It is thought the virus was spread from that individual to members of their household and then to a care home in Lambeth.
Twenty-three cases of the South African variant were detected in the care home – 13 staff and 10 residents.