Boris Johnson explains when coronavirus lockdown will end

The Prime Minister fielded the enquiry, flanked by England's chief medical officer Professor Chris Whitty and chief scientific advisor Sir Patrick Vallance, after announcing that all travel corridors will close from Monday.

This means everyone arriving in the UK will have to self-isolate.

• READ MORE: UK will close all travel corridors on Monday

Appearing via video link, Michael from Cornwall asked what the number of daily Covid-19 cases and deaths would have to fall to for the government to consider lifting some restrictions.

The Prime Minister explained that this was down to several factors, and not just the number of cases or daily death toll.

Mr Johnson said: "The answer is that we want to get to a stage where we're confident that we've vaccinated the Joint Committee on Vaccination and Immunisation (JCVI) 1-4 cohorts  - those in care homes, care home workers, NHS staff, those over 80, those over 70 and so on.

Prime Minister Boris Johnson has said when coronavirus lockdown restrictions could be lifted

"The most vulnerable groups, we've got to do them.

"And then, depending on the effectiveness of that rollout (and, as you know, we're hoping to do all of them by February 15) we'll think about what steps we could take to lift the restrictions.

"But it will also depend on what the disease is and what's happening because what we can't have...is any false sense of security so that we lift the restrictions altogether and then the disease really runs riot in the younger generations.

"And, as you know at the moment, I think about a third of those going into hospital are under 65 and about a quarter are under 55 - from memory.

• READ MORE: Three people slapped with Covid fines after visiting house in Brighton

"So it (Covid-19) can affect and does affect huge numbers of younger people as well, often very badly, and the risk is that those numbers would be greatly inflated if we let go too soon in circumstances where the disease was really rampant.

"That is not to say, Michael, that we don't want or I don't want to try to get to relaxations as soon as we reasonably can.

"But there are a lot of things that have to go right.

"We have to make sure the vaccine programme is working well, we have to make sure there are no new variants or big changes in our understanding of the disease, and we have got to work together to deliver the results of the current lockdown and get the disease under control.

England's chief medical officer Professor Chris Whitty

"There are some signs in some places that that is working, but it's going to take a huge national effort."

England's chief medical officer, Professor Chris Whitty, also addressed the question.

He warned that the country was "not going to move from a sudden lockdown situation to nothing".

"It will have to be walking backwards by degrees, testing what works and then, if that works, going the next step," Professor Whitty said.

He also said there were "indirect effects" of Covid-19 deaths which could result in even greater pressure being placed on the NHS.

• READ MORE: Interactive map shows the areas of Sussex with the highest and lowest coronavirus rates

These included effects on health services dealing with the likes of cancers, cardiovascular diseases and strokes.

Professor Whitty said: "We've not only got to reduce the direct effects, we've also got to make sure of the sufficient ability for the NHS to treat all these other things, or we could have a significant health problem which is a knock-on.

"People not likely to die of Covid but they have very severe Covid and are in hospital, meaning we can't treat other things.

"So we must always think about those other areas of health as well."

Prime Minister Boris Johnson at a coronavirus press conference

Mr Johnson added: "It's not that the death rate isn't important, it is important and we will of course consider it.

"But it is just one of the factors we've got to bear in mind.

"It's the rate of the disease and the risk of another really huge spike of infection as well."