Britons who test positive for Covid with a lateral flow test will have to self-isolate immediately and cannot have a PCR test to confirm their result from today, which critics believe means thousands face being quarantined with false positives.
Previous guidance to confirm positive rapid tests with more accurate lab results has been removed indefinitely because of the Omicron wave.
The UK Health Security Agency said the 'vast majority' of people with a positive LFD result can be confident they have the virus because case rates are so high - but experts admit that around one in 3,000 tests brings a false positive.
And lateral flow tests may be less effective at detecting Omicron even when people are at their most infectious, a US study found last week. It took an average of three days longer for people to test positive on a lateral flow test — which give results in as little as 15 minutes — after their infection had already been confirmed on a PCR test, they found.
The decision to limit PCRs is taking place to free up capacity in laboratories for PCR tests for those who have Covid-19 symptoms.
Confirmatory PCR tests will no longer be allowed for people testing positive for Covid on a lateral flow test
People who receive a positive result on a lateral flow device (LFD) will be required to self-isolate immediately, without requiring PCR confirmation.
On a visit to a vaccination clinic in Uxbridge, Boris Johnson poured cold water on rumours that lateral flow tests could stop being free soon, saying they will stay 'as long as necessary'
The UKHSA insists it is a temporary measure while Covid-19 rates remain high across the UK - but there is currently no end date.
UKHSA chief executive Dr Jenny Harries said: "This is a tried and tested approach. With Covid cases high, we can confidently say lateral flow tests can be used to indicate Covid-19 without the need for PCR confirmation.
"If you test positive on an LFD, you should self-isolate immediately and register your result to allow contact tracing to take place.
"It also remains really important that anyone experiencing Covid-19 symptoms self-isolates and takes a PCR test via gov.uk, or by phoning 119.
"I'm really grateful to the public and all of our critical workers who continue to test regularly and self-isolate when necessary, along with other practical and important behaviours to limit transmission of the virus, as this is the most effective way of stopping the spread of infection and keeping our friends, families and communities safe."
Exceptions to the new rules include people who want to claim the Test and Trace Support Payment, those who are taking lateral flow tests as part of research and those who have a positive day 2 test result after they arrive in England.
Boris Johnson last night piled pressure on Government scientists to approve a further cut to Covid isolation after health chiefs admitted misleading ministers.
The Prime Minister asked the UK Health Security Agency (UKHSA) to look again at whether the self-isolation period could be relaxed from seven days to five to ease crippling staff shortages in the economy and public services.
In an extraordinary twist, the UKHSA yesterday admitted it had issued misleading claims about the way Britain’s rules compare to other countries.
