Bars and restaurants should stay shut until May, researchers have suggested, as they warned that reopening society too quickly could have a 'disastrous' effect.

A team of experts modelling the pandemic said that even if 90 per cent of people are vaccinated against coronavirus, 10 per cent would still be at risk of serious infection.

They argued that little is currently known about the effect of vaccines on transmission and if younger people catch coronavirus - they would be at risk of long Covid.

For these reasons the experts said they believed that restrictions should be lifted slowly, with various scenarios modelling what would happen if lockdowns lasted until the winter.

Releasing all measures at the end of April once all over-50s, those in high risk groups and frontline health and social workers are vaccinated, could still lead to a huge surge in cases, they said.

Dr Marc Baguelin, from Imperial College London, who sits on the Scientific Pandemic Influenza Group on Modelling, a sub-group of Sage, said the premature opening of the hospitality sector would lead to a 'bump' in Covid-19 cases.

He said: "We looked at the partial reopening and the increase in the R number - it will generate an increase in the R number - the extent of which we don't know really.

"Something of this scale, if it was to happen earlier than May, would generate a bump in transmission, which is already really bad.

"So you have a lot of pressure on hospitals, you will have another wave of some extent.

"At best you will keep on having very, very unsustainable level of pressure on the NHS."

Instead, modelling indicates that a more gradual relaxation of controls is far less risky, and could provide an exit without overwhelming the health service.

Mark Woolhouse, professor of infectious disease epidemiology at the University of Edinburgh, said: "Ninety percent coverage of any group, but we're talking about the most vulnerable group, which is about 10 million people.

"That means one million people not vaccinated.

"And that is more people in that group than have already had the infection.

"So it's clear, there is the potential for a bigger epidemic at some stage."

He added: "The possibility, we can't reach - not herd immunity, we'll always have some herd immunity - but the herd immunity threshold can't be reached, yes that's a realistic possibility and the new variant makes that more likely."

The University of Edinburgh study assumed 85% vaccine uptake, and delivery of two million doses a week following the vaccine priority groups.

A separate study from the University of Warwick also modelled possible scenarios, but did not make predictions.

Researchers say, that under the most optimistic assumptions about vaccine rollout, coverage and efficacy, it will be several months before the population immunity threshold is reached in the UK.

Matt Keeling, professor of populations and disease at the University of Warwick, said one scenario the model considered was the complete relaxation of all control measures in April when there has been three months of vaccination and 30 million doses.

He said: "Completely stopping all controls is disastrous, we get massive peaks of both daily deaths and hospital admissions.

Prof Keeling added that no one is suggesting relaxing all measures immediately would be a viable strategy, as cases would increase very rapidly, and as soon as that started to happen, control measures would be reinstated.

He explained: "But it just shows that even at that point, you can't relax, even at 30 million doses."