Surge testing is being deployed in Croydon after the patient who contracted the Brazilian variant was finally found.
The mystery infected person has been found after numerous cases of the variant of concern were detected in the UK.
At a press conference tonight Health Secretary Matt Hancock said surge testing was now being deployed in Croydon.
Patient X’s location has not been reported by officials.
Mr Hancock added the incident team at Public Health England who assessed the case do not believe there was any further transmission from the patient.
Six cases of the P1 variant, first identified in the Brazilian city of Manaus, have been found – three in Scotland and three in England.
A public appeal was made for one of those people in England to come forward after they took a test in February but left no contact details.
The P1 variant, which was also detected in travellers from Brazil to Japan, was associated with a surge of cases in Manaus late last year.
It is among a total of four variants of concern being tracked by scientists in the UK.
A study this week suggested that between 25 per cent and 61 per cent people in Manaus who had previously had Covid were susceptible to reinfection with the concerning P1 variant.
The variant carries a mutation in the spike protein called E484K, raising concerns that vaccines may not be as effective against it.
On Monday, surge testing began in South Gloucestershire after two cases of the Manaus variant were detected in one local household which had a history of travel to Brazil.
News of the tracing of the mystery infected person comes as new data showed the number of people with Covid-19 in homes across England continues to fall – although the picture is uncertain in some regions.
Figures from the Office for National Statistics (ONS) estimate that around one in 220 people in private households in England had Covid-19 between February 21 and 27 – the equivalent of 248,100 people.
The figure is down from around one in 145, or 373,700 people, for the period February 13 to 19, and is the lowest figure since the week to October 1, when it was one in 240.
However, the number of people infected in England is still high when compared with last summer.
In the week to August 25, around one in 2,000 people had coronavirus.