Prime Minister: "The tide can be turned in the next 12 weeks"

"I'm conscious as the days have gone by that people will want to know how long we're expecting them to keep it up," he told his daily press conference in No 10.

"I think, looking at it all, that we can turn the tide within the next 12 weeks and I'm absolutely confident that we can send coronavirus packing in this country.

"But only if we all take the steps that we've outlined, that is vital, that's how we're going to reduce the peak and once we've achieved that and I think that we will, if we take the steps I've said, then the scientific progress that we've been making will really start coming into play."

Mr Johnson thanked the public for the "huge efforts" they have taken in complying with the advice for the battle against Covid-19.

"We're asking students to put their education on hold, we're asking people not to socialise in the normal way and already we can see the impact this is having on the UK economy and on business, on great, great companies," he said.

"So it's vital that we in Government stand behind them when what we are asking everyone to do is so crucial for saving literally thousands of lives by fighting this virus."

Mr Johnson said: "UK experts, scientists, expect to start trials for the first vaccine within a month. And above all we're getting better at testing."

He added: "To give you an idea of what is coming down the track, we're in negotiations today to buy a so-called antibody test, as simple as a pregnancy test which can tell whether you have had the disease and it's early days, but if it works as its proponents claim, then we will buy literally hundreds of thousands of these kits as soon as practicable.

"Because obviously it has the potential to be a total gamechanger."

Mr Johnson said: "By the same token we're massively increasing the testing to see whether you have it now and ramping up daily testing from 5,000 a day, to 10,000 to 25,000 and then up at 250,000."

Mr Johnson added: "That knowledge of where the virus is will make a huge difference to our management of the disease and our ability to reduce disruption and economic difficulty."

He said: "It's by this combination of ruthless, determined, collective action and scientific progress that we're already seeing that we will succeed.

"And I know how difficult it may be or it may seem right now, but if we do this together, we will save as I say many, many thousands of lives."

Mr Johnson said: "I say to business, stand by your employees, stand by your workers, because we will stand by you."

Chief medical officer Professor Chris Whitty warned there will be a "lag" before the public's efforts to stem the spread of Covid-19 will result in a slowing of case numbers.

"At the moment London from the coronavirus is under pressure but indirectly, but that's going to go up," he said.

"The first thing that will get under the greatest pressure will be intensive care and respiratory care system, that's the first point of real pressure on the NHS that's going to be happen.

"And to be clear: even if everybody does all the things we hope and really, really would ask that they will do, the numbers will continue to go up over the next two weeks because there's a lag until things start to improve."

Mr Johnson said: "On mass buying and the price issue, I really hope that retailers will continue to be reasonable. I certainly wouldn't want to see profiteering of any kind."

He added: "As I said before, we've got good supply chains farm to fork - there's no reason for the shops really to be empty.

"Please be reasonable, please be reasonable in your shopping, be considerate and thoughtful for others as you do it".

Prof Whitty said: "On the antibody tests we should be clear that although we're confident there will be antibody tests, we're not absolutely confident yet about whether the ones that are currently on the market are the right ones and that needs to be tested out.

"And that's something that is an absolute priority for Public Health England.

"But once we have these, the key thing for in the first case health care workers and then other workers and members of society, we'll be able to say to somebody, you've had this virus, you're not likely to get it again at least in the immediate term, and now we can be confident you can return to work and now we can be confident you don't need to be taking some of the precautions you've been taking to date."

He added that "there will be a while before we've actually got this in large enough numbers" and it is "more useful" the further along in the outbreak.