The UK is "very close" to having a Covid-19 test that can tell if someone has already had the respiratory disease and it immune to it, the Government's former chief scientific advisor has said.

The science and technology allowing the development of this test is progressing "at the speed of light" compared to how it would have several years ago, Professor Sir Mark Walport told ITV's Peston.

The Chief Executive of UK Research and Innovation said that such a test would be "very important" as it would allow health care workers to be tested to see if they are immune to coronavirus, having already had the respiratory disease, allowing them to work with those who are infected.

Sir Mark said he did not know exactly when such a test would be available, but it would "role out quickly".

Earlier on Wednesday, the current Chief Scientific Advisor said Public Health England’s (PHE) work on the antibody test is "progressing very fast", and will provide valuable insight into the pandemic.

Speaking at the daily Downing Street press conference, Prime Minister Boris Johnson added that development of the test was not far away.

Sir Patrick added: "That’s progressing very fast, Public Health England are looking at this today.

"They’ve got a test in house they’ve got going and we’re looking at ways at getting the much more widespread version out.

"It is a game-changer.

"And the reason it’s a game-changer is that it allows you to understand the proportion of the asymptomatic population – who’s had this disease, but hasn’t had symptoms.

"Going forward it’s going to be critically important to be able to monitor this disease well because only by being able to monitor it can we start relaxing measures again."

Sir Patrick Vallance said such a test would be a 'game changer'. Credit: PA

Earlier on Wednesday, the Government announced that it would be ramping up its testing efforts, carrying out 25,000 coronavirus tests per day.

On Tuesday, head of the World Health Organization, Dr Tedros Adhanom Ghebreyesus said one of the best ways to beat Covid-19 is to "test, test, test" people.

Also on Peston, Sir Mark said the Government was "well prepared" to deal with a pandemic, but had come under criticism for its response to coronavirus because it cannot prepare for every eventuality.

"There are so many potential disasters, you can't absolutely have everything in place for every one of them," Sir Mark told ITV News' Poltical Editor Robert Peston.

When questioned if there were enough ventilators to help the most ill breathe, Sir Mark said "retrospect" was "very powerful" but since "every epidemic is different" the equipment needed for an infinite number of scenarios was impossible to stockpile.

However, he added that manufacturers were being "mobilised" to producer more.

It is thought the UK currently has access to around 12,000 ventilators.

Sir Mark continued researchers and modellers had been working on Covid-19 since its outbreak and working on the best time to introduce new measures.

The 67-year-old added the Government was globally "unique" in following scientific advice but like with all epidemics there is no "pre-defined road map" for "precisely what you do".

Coronavirus: Everything you need to know: