New Covid cases in the UK averaged nearly half a million a day in the week after Christmas, almost three times the official figures, new analysis suggests.
Meanwhile, health agencies have urged caution about interpreting the regular case numbers published each day for the UK, following changes in rules about testing.
An average of 173,400 new cases of coronavirus per day were recorded from December 26 to January 1, according to the government's Covid-19 dashboard.
