The UK government is expanding its COVID-19 Test and Trace plan to cover all secondary school students aged between 11 and 18 in and around London, as the city registered a spike in coronavirus infections in recent days.
UK Health Secretary Matt Hancock has said that more details of the so-called "surge testing" programme will be set out on Friday after the fastest rise in infections was noted among secondary school age children.
This group will now be prioritised for testing by the National Health Service (NHS) in the seven worst affected boroughs of London, in parts of Essex that border London, and parts of Kent.
"Looking into the detail, the testing results and surveys show us that by far the fastest rise is among secondary school age children, 11 to 18 year olds, while the rate among adults in London is broadly flat," he said, during a 10 Downing Street briefing in London on Thursday evening.
"But we know from experience that a sharp rise in cases in younger people can lead to a rise amongst more vulnerable age groups later. We've seen that happen before. So we need to do everything we can to stop the spread among school-age children in London right now," he said.
The UK government is scheduled to review the current tiered system of coronavirus lockdown restrictions next Wednesday, when it will decide whether London and its suburbs need to be moved from the current high alert level of Tier 2 to the very high alert level of Tier 3.
The latter would mean hospitality venues only serving takeaway meals and almost any mixing between households being banned.
"We must not wait until the review which will take place on the 16 December. We need to take targeted action immediately," said Hancock.
"Having spoken to the leaders of London's councils, and to the mayor [Sadiq Khan], we have decided to put in place an immediate plan for testing all secondary school aged children in the seven worst affected boroughs of London, in parts of Essex that border London, and parts of Kent," he said.
The minister said that schools will be kept open to not disrupt classes too much but officials will be working with schools and local authorities to encourage secondary school children and their families to get tested over the coming days through mobile testing units.
"I want to urge all those involved to step forward for testing. It is important that 11 to 18 year-olds get tested in these boroughs irrespective of whether they have symptoms - this is a really important point, because we know that you can have COVID - and you can still pass it on - even without symptoms," added Hancock.
The NHS Test and Trace programme has been conducting lateral flow rapid result tests in targeted regions and sectors, such as universities. The move to expand the programme comes at the end of a week which marked the first rollout of the Pfizer/BioNTech vaccine against COVID-19.
Hancock welcomed the "help on the horizon" offered by the vaccine but urged people to continue to follow lockdown rules and not "blow it now" because the fall in the number of cases has "flattened off", even as numbers begin to rise in and around London.
The warning comes as the UK recorded another 516 deaths from the deadly virus, taking the country's death toll past 63,000.