Boris: Tide can be turned in the coronavirus Covid-19 fight within 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 Number 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."

The Government had yet to announce a list of what it considers 'key workers' this afternoon, after saying their children will be looked after by schools - which will close to the majority of pupils tomorrow - so they can go to work.

They will be NHS staff, police officers, and delivery drivers, though a finalised list was yet to be released.

GCSE, A level, and Sats exams will not go ahead this summer, Mr Johnson announced yesterday, though he said those who need qualifications will get them.

More details are expected to be released tomorrow.

Alistair Jarvis, chief executive of vice-chancellors’ group Universities UK, said that if exam grades cannot be awarded as usual, then one option may be to give university places based on an assessment of things such as an applicant’s predicted grades and personal statement.

“I think that’s doable,” he said. “It is not preferable as it is very tricky.”

A further 29 people who tested positive for Covid-19 have died, NHS England said earlier, bringing the total number of confirmed deaths nationally to 128. There have been 137 deaths in the UK.

NHS England said: “Patients were aged between 47 and 96 years old and had underlying health conditions. Their families have been informed.”

None were in Lancashire, where there were 15 confirmed cases at the last official count. Blackpool had four.

Nationally, there are more than 2,600 confirmed cases, though the real figure is feared to be higher than 55,000, with tests only being carried out in hospitals.

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."