Scientists advising the Government have said lockdown should not be lifted too quickly after Tory lockdown-sceptics called for a complete removal of restrictions by the end of May.

Professor Graham Medley, chairman of the Scientific Pandemic Influenza Group on Modelling (Spi-M), said ministers should “make decisions dependent on the circumstances, rather than being driven by a calendar of wanting to do things.”

He was backed by Dr Mike Tildesley, also from Spi-M, who said there needed to be a gradual easing out of lockdown to prevent a resurgence of cases and the need to implement tighter controls.

It comes after former health secretary Jeremy Hunt told the Guardian that ministers should take a cautious approach to lifting the lockdown so that new coronavirus cases can be driven down to 1,000 a day.

Speaking to BBC Radio 4’s Today programme in a personal capacity, Prof Medley said watching case numbers was still important even though vaccines would protect the elderly and most vulnerable.

“Vaccination offers a way out and does reduce the impact of infection, but it doesn’t remove it completely,” he said.

“And so case numbers are still important because they represent the risk of having to go back into some kind of national measures.”

Asked whether case numbers needed to be as low as 1,000 a day, he said: “Clearly the lower the numbers of cases are, the more time you have to react if things start to go badly wrong.

“If the case numbers are very high, if they’re as high as they are at the moment, for example, then you will have very little time in which to react to avoid the kind of national lockdown that we’re in at the moment, which nobody wants.”

Dr Tildesley told Times Radio it was important “to avoid a yo-yo situation where we unwrap things too rapidly, we get a resurgence and we have to lock down again”.

He added: “The real concern here and where we really need to be careful is that it all comes down to R number.

“As soon as we start to relax, things go up. The key thing for me is we need to get our children back to school first – that’s clearly the most important thing.

“But I would really encourage it needs to be gradual stepping out of lockdown so that we don’t get a resurgence as we move into the spring.”

Pressed on whether outdoor socialising next month seemed reasonable, he said “a little bit more mixing outdoors” might be reasonable but would need “very clear messaging from the Government”.

He added: “I really appreciate the need for people getting back some level of normalcy. My concern is a resurgence by doing that, which will lead to a much greater problem as we get into the spring.”

Dr Tildesley said the Government would need to look at national case rates per day for unlocking, as well as local rates, plus hospital occupancy and the R rate.

“I think we need to look at all of these indicators – if they get as low as possible we can really prevent the risk of the resurgence, then I think that’s the point to unlock.”

Speaking to the BBC news channel, Dr Ian Higginson, vice president of the Royal College of Emergency Medicine, said his organisation “could not be more firmly in camp caution… this could all go Pete Tong really easily”.

On Thursday, Mark Harper, chairman of the Covid Recovery Group of lockdown-sceptic backbenchers, said all restrictions should be lifted once the first nine priority groups – including all over-50s – have received their first vaccine dose.

Asked on BBC Radio 4’s World At One when he saw “life returning to normal”, he said: “I think it’s paced with vaccine rollout.

“Back-of-the-envelope calculations that I did based on two million doses a week, you could get the top nine (priority) groups, first doses, and the top four groups, second doses, all done by the end of May.

“So it seems to me by the time you get to the end of May, no later than that, you should be in a position to get rid of restrictions completely.

“But obviously it does depend on the rollout of the vaccine.”

Sir Graham Brady, the chairman of the backbench 1922 Committee, has also said the Government is in danger of falling out of step with public opinion if it delays the opening of schools in England to March 8 as planned.

In his interview with the Guardian, Mr Hunt, who is chairman of the health select committee, said the Government should aim to suppress Covid cases so that intensive contact tracing can work.

Mr Hunt said: “The Koreans and the Taiwanese have kept their economy open. All their restaurants are open, because they’ve kept case transmission low, and we just need to do what it takes to get to that point. And for me, where I’m at on that is that you just need to get it down to 1,000 new infections a day or less.”