UK Prime Minister Boris Johnson has vowed to ramp up the country's coronavirus testing efforts after facing a barrage of criticism for screening fewer people than other nations at a similar stage of the epidemic.

The number of deaths linked to the coronavirus reached a new UK high on Tuesday, the latest figures available, with 563 deaths recorded in a day, taking the total to 2,532.

The spike in deaths came as the British Medical Association (BMA) released new ethics guidelines for doctors that mean older patients with a low chance of survival could have life-saving ventilators removed so the machines can be given to healthier patients.

Newspaper headlines on Thursday blasted the government's failure to test more, even in typically-loyal British media outlets. "Why mass testing must be our No 1 priority -- and why we lag behind the rest of the world," said the Telegraph's front page.

Paul Cosford, emeritus medical director of public Health England, told Sky News on Thursday that the UK was testing nearly 15,000 people a day and aims to reach 25,000 a day by the middle of April. Only "about 2,000" frontline National Health Service (NHS) workers have so far been tested for the virus, he said.

The latest figures come eight days after Johnson asserted that the UK was "massively ramping up" its nationwide testing program, and would continue to increase the number of tests carried out each week. The Prime Minister, who is himself in self-isolation after testing positive for the virus, posted a video to Twitter on Wednesday evening in which he lamented a "sad, sad day" in reference to the latest death toll.

He stressed his efforts to increase the country's testing capacity, as well as listing the measures already put in place to deal with the pandemic and urging people to respect the restrictions currently in place.

"I want to say a special word about testing, because it is so important, and as I have said for weeks and weeks, this is the way through," Johnson said. "This is how we will unlock the coronavirus puzzle. This is how we will defeat it in the end."

Shortage fears

Earlier Wednesday, UK Business Secretary Alok Sharma said during the country was looking to grow its testing capacity from 10,000 a day to hundreds of thousands.

Germany's leading virologist Christian Drosten said last Thursday that his country was carrying out 500,000 tests a week.

Prof. Cosford said Public Health England was in contact with its peers in Germany as the UK seeks to step up its coronavirus testing capacity.

"I absolutely accept that we need to build this further. There is a lot of work that is going on in order to get this testing capacity in place," Cosford said. "We're in constant discussions with colleagues in Germany -- and other countries -- around what they're doing, where their sources are coming from, what their supply system is. Of course we need to build this further."

Chief Medical Officer Chris Whitty warned last Wednesday that the UK did not have "sufficient testing" capabilities to identify cases, telling reporters that there was a "global shortage" of available tests.

UK health workers have also voiced concerns that personal protective equipment and some medical supplies are running low.

Older, sicker patients could lose ventilators

The BMA said its new guidance had been prepared for doctors who will need to make "grave decisions" about who should receive "scarce lifesaving resources" if the country's health system is overwhelmed by coronavirus cases.

"As such, some of the most unwell patients may be denied access to treatment such as intensive care or artificial ventilation," the BMA's ethics guidance note states.

"This will inevitably be indirectly discriminatory against both the elderly and those with long-term health conditions, with the latter being denied access to life-saving treatment as a result of their pre-existing health problems."

It says imposing an age cut-off would be illegal, but adds that older patients with pre-existing respiratory problems would have a "very high chance of dying despite intensive care," and are therefore lower priority for admission.

The UK government has previously warned the country's health system could be overwhelmed if strict social distancing measures are not followed.

A converted convention center in London is due to start operating this week as a massive field hospital for coronavirus cases and could soon be the biggest intensive care unit in the country.

And a temporary mortuary is being built in east London as the death toll from coronavirus in the city continues to grow.

In a letter to residents, the Mayor of Newham Council, Rokhsana Fiaz, said the mortuary is being built in the Manor Park area because it is close to a cemetery and crematorium.

"The facility will act as a holding point before a respectful and dignified cremation or burial can take place to send a loved one on their final journey. Sadly relatives will not be able to visit the site," she said in the letter.