Urgent testing for the South Africa variant of coronavirus is beginning in parts of England, after cases were found with no known links to travel or previous cases.
Two cases were found in Surrey, and testing will also take place in London, Kent, Hertfordshire and Walsall.
Previous cases in the UK were traced back to South Africa.
Cases caused by the variant were identified as part of Public Health England’s random checks on tests.
The agency has been testing 5% of all positive cases, which has thrown up a number of cases that were not directly linked to people who had travelled to South Africa, prompting fears there may be community transmission of the virus.
It is not known how many cases have been identified.
The government has now ordered mobile testing units to be dispatched to a number of neighbourhoods where these cases have been identified.
In the Surrey town of Woking, home testing kits will also be sent to households.
Positive cases will be analysed to see if they are caused by the South African variant.