At least one in eight people in England had had COVID-19 by December last year, new survey data estimates.
The figures for private households come from the Office for National Statistics COVID-19 Infection Survey in partnership with the University of Oxford, University of Manchester, Public Health England and Wellcome Trust.
They are based on the proportion of the population who are likely to have tested positive for antibodies to COVID-19, based on blood test results from a sample of people aged 16 and over.
The ONS says the figures equate to approximately 5.4 million people in England having previously had the infection.
Antibody data on infection in private households suggests that one in 10 in Wales had also been infected by December, alongside one in 13 in Northern Ireland and one in 11 in Scotland.
The ONS found "substantial variation" between regions in England, with 17% of people in private households in Yorkshire and the Humber estimated to have tested positive for antibodies in December, compared with 5% in southwest England.
In London, the figure was 16% in December, up from 11% in October, while it was 15% in the North West, up from 6% in October.
The percentage testing positive for antibodies in each region was as follows:
Yorkshire and the Humber 16.8%
London 16.4%
North West 15.1%
West Midlands 14.3%
East Midlands 12.7%
North East 12.5%
South East 8.3%
East of England 8.1%
South West 4.9%
Experts have warned that the length of time coronavirus antibodies are detectable in the blood is not known.
The ONS study measures antibodies in people who live in private households across the UK. It does not include those in hospitals, care homes or other institutional settings.
The study came as Health Secretary Matt Hancock revealed he is self-isolating after receiving an alert through the NHS COVID-19 app.
In a video posted on Twitter, he said: "Last night I was pinged by the NHS coronavirus app, so that means I'll be self-isolating at home, not leaving the house at all until Sunday."