The government is facing growing pressure to ramp up coronavirus testing, as the UK saw its biggest daily increase in deaths.
Some 2,352 virus patients had died in hospital as of 17:00 on Tuesday - up 563 in a day, the latest figures show.
Prime Minister Boris Johnson said testing was "massively increasing" and it was "the way through" the pandemic.
Meanwhile a major international climate meeting, COP26, is the latest event to be postponed as a result of the virus.
The climate talks were due to take place at Glasgow's Scottish Events Campus in November - which is being turned into a temporary field hospital to treat coronavirus patients.
The UN's climate body, the UNFCCC, and the UK government said the summit would be pushed back to 2021.
In a video message posted on Twitter, the prime minister said Wednesday had been a "sad, sad day" due to the high number of deaths in the UK.
Mr Johnson, who is self-isolating in Downing Street after contracting the virus, also reiterated the government's commitment to "ramp up" testing.
He said: "This is how we will unlock the coronavirus puzzle. This is how we will defeat it in the end."
'Hundreds of thousands' of tests promised
The government has been under pressure to increase the screening of medics, so that those who are self-isolating unnecessarily can return to work.
More than 3,500 NHS frontline staff in England and Wales have been tested for the virus since the outbreak began.
But cabinet minister Michael Gove said a shortage of chemicals needed for the tests meant the NHS - which employs 1.2m in England - could not screen all workers.
The prime minister's official spokesman said the government was working with NHS England, Public Health England and other organisations to boost test capacity with an additional network of labs and testing sites.
Dr Yvonne Doyle, Public Health England medical director, told a daily coronavirus briefing in Downing Street that there was currently capacity for about 3,000 tests a day for frontline NHS staff.
She said the "intention" was for testing for frontline staff to increase from "thousands to hundreds of thousands within the coming weeks".
'Up-tick' in car journeys
The World Health Organization has said the world is set to reach one million confirmed cases and 50,000 deaths worldwide in the next few days.
Dr Doyle said the UK was not in "as severe" a position as Spain, the US or Italy, but added there was "no reason to be complacent".
She said while the spread of the virus was most advanced in London, the Midlands was "obviously a concern" too.
As of 9:00 on Wednesday, 152,979 people in the UK had been tested for the virus with 29,474 confirmed positive.
This includes 4,139 cases in the Midlands and 8,341 in London.
Dr Doyle added while use of public transport had gone down since the government enforced social distancing measures, an "up-tick" in motor vehicle use in the last 24 hours was "slightly concerning". She urged members of the public to stay home to "protect the NHS".
The number of questions about the lack of testing at the daily press conference came as no surprise. The government has been heavily criticised for not increasing testing capacity more quickly.
Dr Doyle said she was confident the UK would achieve the target of 25,000 tests a day by the end of the month.
There is some way to go - over the past 24 hours just shy of 10,000 tests have been done.
The lack of tests means NHS staff have had to self-isolate at home when members of their household show symptoms.
News that there are going to be five drive-through centres for staff will also help.
But it was interesting Dr Doyle was also asked by how much more testing can be increased by in the long-term.
If the number of cases does come down, testing will play a crucial role in allowing the lockdown to be eased.
The plan would be to contain the virus by testing lots of people quickly. That will require the UK to be able to tests hundreds of thousands of people a day.
A doctor who came out of retirement to volunteer for the NHS has become the fourth UK medic to die with the virus, which causes the disease Covid-19.
Dr Alfa Sa'adu, 68, had been volunteering at Queen Victoria Memorial Hospital in Welwyn when he contracted coronavirus.
His son Dani Saadu posted online that his dad had died after "fighting the virus for two weeks".
"My dad was a living legend, worked for the NHS for nearly 40 years saving people's lives here and in Africa," he said.
The BBC's head of statistics Robert Cuffe said the latest increases in the number of patients dying with coronavirus balance out with the below-average rises on Sunday and Monday.
He said the number of new deaths has been increasing at a slightly slower rate than earlier in the epidemic, "but if that keeps up, we'd expect to see in the region of a thousand deaths a day by the weekend".
Downing Street said 390 million pieces of personal protective equipment (PPE) including masks, alcohol wipes and aprons, have been delivered to NHS staff over the last two weeks.
The prime minister's official spokesperson said the government was working with a number of suppliers which had come forward with offers of PPE, or proposals to manufacture more.
It follows criticism from some frontline workers over the lack of protective equipment, with staff at one hospital in Essex warning they could "limit services" to patients with coronavirus "to a bare minimum" over fears for their own safety.
The prime minister's spokesperson also said the NHS will be sent 30 new ventilators next week and promised "hundreds" more would follow.
The NHS is reported to have 8,175 ventilators and the government believes up to 30,000 ventilators could be needed at the peak of the pandemic.
In other developments:
- Business Secretary Alok Sharma has issued a stark warning to banks, after concerns that up to a million companies could fold because they could be denied emergency loans
- Commons Speaker Sir Lindsay Hoyle has written to Jacob Rees-Mogg, Leader of the House of Commons, to ensure Parliament can operate "virtually" in the event social distancing measures remain in place on 21 April, when MPs plan to return to work
- Defence Secretary Ben Wallace became the fourth cabinet minister to have to self-isolate
- In the past 15 days, NHS 111 has responded to more than 1.7 million inquiries from people concerned they might have symptoms of coronavirus
- Wimbledon has been cancelled for the first time since World War Two because of the pandemic
- All Champions League and Europa League matches have been suspended "until further notice" by Uefa
- The Edinburgh Festival, due to take place in August, has also been cancelled
- New research suggests a loss of smell or taste may be a sign that you have coronavirus
- The DWP say there have been 950,000 new Universal Credit claims from the mid-March shutdown until 31 March - the normal figure for a two-week period is 100,000
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