LONDON (REUTERS) - British Prime Minister Boris Johnson vowed to ramp up testing for coronavirus, saying it was the key to defeating the outbreak after his government faced criticism for testing much fewer people than some of its European peers.

Britain, which initially took a much more restrained approach to the coronavirus outbreak, has faced widespread criticism that it was carrying out far too few tests, particularly for front-line staff in the National Health Service.

"We're also massively increasing testing," Mr Johnson said in a video message from a flat in Downing Street, where he is self-isolating after testing positive himself. "I want to say a special word about testing because it is so important.

"As I have said for weeks and weeks, this is the way through: this is how we will unlock the coronavirus puzzle, this is how we will defeat it in the end," he said.

While Germany has been testing about 500,000 people a week, Britain's current capacity is just about 12,750 a day, a figure the government said it was aiming to double by mid-April.

"What we need to do is massively ramp up not just tests so that you can know whether you have had the disease in the past - so-called antibody tests - so that will enable you to go to work in the confidence that you can't be infected or infectious," Mr Johnson said.

"Second, people need to know whether they haven't got it rather than isolating themselves at home for no reason, and that's very, very important above all for our NHS staff," he said.

Ministers have suggested that shortage of necessary chemicals had been a factor, although the industry has said if necessary, reagents can be manufactured and delivered to the NHS.

The United Kingdom's coronavirus death toll rose 24 per cent to 2,921 as of April 1.

As of 0800 GMT on April 2, a total of 163,194 people had been tested of which 33,718 tested positive, the health ministry said.

"Of those hospitalised in the UK who tested positive for coronavirus, 2,921 have sadly died," the ministry said.

NHS England said that of the 561 people who died in English hospitals in the previous 24-hour cycle, 44 had no underlying health conditions. The age range of those without underlying health conditions was 25 to 100 years old.

The United Kingdom has one of the worst official death tolls in the world, after Italy, Spain, the United States, France, China and Iran.

It has led to accusations that Britain had been too slow to prepare for the outbreak.

Its approach to countering the virus was abruptly changed after modelling showed that a quarter of a million people in the United Kingdom could perish, leading to more stringent measures.