Boris Johnson said he has "no doubt" the UK will "turn the tide" on Covid-19, in a video update from isolation yesterday.

The Prime Minister insisted that increased testing was "how we will unlock the coronavirus puzzle".

The government has been under pressure for weeks to increase testing for coronavirus: around 152,979 people have so far been tested, with testing mainly confined to those admitted to hospital, and just 2,000 out of 500,000 frontline NHS staff tested.

This policy has been criticised by health experts, including Anthony Costello, British ex-director of the World Health Organization (WHO), as the international health body urged countries like the UK to "test, test, test".

But in a video recorded from self-isolation on Wednesday night, Mr Johnson said: "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. This is how we will unlock the coronavirus puzzle.

"This is how we will defeat it in the end."

He promised to "massively ramp up" anti-body testing, which can show whether or not people have already had the virus, and testing for those isolating with potential symptoms, who might not in fact have the disease.

And he promised a further 397 million pieces of personal protective equipment would be sent out to NHS staff.

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The Prime Minister opened his self-recorded update from isolation with a tribute to those who had died after testing positive for the virus, in what was the most deadly day of the outbreak so far in Britain.

He said: "This has been a sad, sad say, 563 more cases, a record in a single day, our thoughts go out to the families of the victims and all their friends.

"But let's be in no doubt, if we can follow the programme that we are currently set up, if we can comply with the measures that we've embarked on together then I've absolutely no doubt that we will begin to start to push those numbers down, and we will turn the tide of the coronavirus over the course, as I say, of the next few weeks and months."

And he ended with reassurance that although he is self-isolating in 10 Downing Street, he remains in "constant touch" with officials to coordinate the coronavirus response.

"I am absolute confident that we will beat it and we will beat it together, and we will do it by staying home, protecting our NHS and saving lives," he said.