Britain has reported its highest daily jump of 381 deaths from the coronavirus, taking its total to nearly 1800.
The 27-per-cent rise in deaths on Tuesday was partly due to the inclusion of a few dozen deaths outside hospitals that were not previously included in Britain's COVID-19 data, according to the government.
The total number of confirmed infections rose to 25,150 from 143,000 people tested, but government health experts estimate that hundreds of thousands of people are probably infected.
Health authorities have tested an average of about 7500 people each day over the past week, falling short of the government's target of at least 10,000 tests.
Cabinet minister Michael Gove, standing in for Prime Minister Boris Johnson, told reporters the government "must go further and faster" in its much-criticised testing programme.
Gove added that the shortage of a chemical reagent was one factor behind the slow increase in testing.
Johnson, who is infected with the coronavirus and self-isolating, has ordered everyone to stay at home except for trips for food shopping, medical needs or one form of exercise per day.
He has urged people not to buy more than they need and promised to co-operate with retailers to maintain essential supplies amid panic-buying and apparent hoarding by consumers.
Analysts reported earlier on Tuesday that British supermarket sales had soared by nearly 21 per cent this month.
Market analysts Kantar said March was "the biggest month of grocery sales ever recorded" in Britain, which imposed a near-lockdown last week to curb the spread of the coronavirus.
"It has been an extraordinary month and social-distancing measures have had a profound impact on all our daily lives - from the way we work and socialise, to how we shop and care for our loved ones," wrote Fraser McKevitt, Kantar's head of retail and consumer insight in Britain.
Goods including flour, oil, cereals, pasta, rice, eggs, coffee, alcohol, toilet rolls and hand sanitiser are in short supply or absent from many supermarket shelves.
Most retailers are imposing queuing and social-distancing measures and limiting customers to buying just one or two items of high-demand products.
Australian Associated Press