The death toll rose to 2,352, a jump of 563 from Tuesday’s official death toll of 1,789.
The previous biggest daily increase, according to Department of Health figures, was 381 on Tuesday.
Wednesday’s death toll alone accounts for 31% of the total number of deaths. The first was recorded on 5 March.
Meanwhile, the Department of Health said 29,474 people have now tested positive for COVID-19 in the UK. This is an increase of 4,324 since Tuesday.
Again, this is the highest day-on-day increase in cases since the first two were confirmed on 31 January. The previous highest daily jump was 3,009, recorded on Tuesday.
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It came as Downing Street said just 2,000 frontline NHS England staff have been tested for coronavirus.
Around 1.2 million people work for NHS England in total.
Boris Johnson’s official spokesman said: “We’re very clear that we want more testing to be carried out, and that we are working with NHS England, Public Health England and others to ensure that happens.”
Among members of the public, Downing Street said the current coronavirus testing capacity stands at 12,750 – but only 8,630 tests were carried out on Monday.
“The NHS and Public Health England are working to increase the capacity,” the spokesman added.
Asked when the UK started placing orders for key coronavirus test components, the spokesman said: “We’ve been working with industry throughout.
“But as the chief medical officer and deputy chief medical officer have both set out, there is a global demand for reagents.
“It’s clear from industry that they are working as hard as they can in order to support the NHS, and we are working alongside them.”