High levels of Covid-19 vaccination rates could "challenge the virus" to mutate into variants against which the jab is less effective, a Government advisor has warned.
After the government announced that all legal coronavirus restrictions will be dropped on July 19, there have been fears it could be "dangerous" to return to life as it was before as the number of cases continues to rise.
Dr Mike Tildesley, a member of the Scientific Pandemic Influenza Group on Modelling (Spi-M) Government advisory panel, told Times Radio that "there is a risk" with the planned reopening.
As more people test positive for Covid-19, Professor Helen Stokes-Lampard, chairwoman of the Academy of Medical Royal Colleges, has also warned the number of deaths is beginning to rise again.
She told BBC Radio 4's Today programme: "We've only just heard in this bulletin about the rising numbers of cases, the rising numbers of people requiring hospital treatment, in intensive care and sadly deaths are starting to rise again, too."
"There seems to be a misapprehension that life will return to normal from then (July 19), and that we can throw away all the precautions, and frankly, that would be dangerous."
The rate of new cases of coronavirus in most areas of England is now back at levels last seen during the winter.
Patient numbers have risen to levels last seen around three months ago.
And there has been a slight increase in the average number of deaths reported each day of people in England who died within 28 days of testing positive for Covid-19.
But this is still far below the sort of numbers seen in January and February of this year.
Dr Tildesley said it was not for him to say whether the reopening should go ahead, but added: "What I will say is it's a very difficult decision for the Government."
When it was suggested to him the UK is living in a "bit of an experiment" in relation to lifting most restrictions, he told Times Radio: "In a sense we are.
"But also I think when we compare with most other countries we do have much higher levels of vaccine rates than most other countries."
He urged people to ensure they get their second dose of vaccine due to the "much higher" levels of protection it provides against the Delta variant.
He said the risk "should decrease as we go through August and we get more people vaccinated."
However, he added: "But still, there is a risk with July 19 in terms of exposing more people to infection as a result of further reopening."
Dr Tildesley warned: "Of course the more cases you have, particularly with high levels of vaccine protection, that does then kind of challenge the virus a little bit more and gives more potential for it to mutate into a form where the vaccines are less effective."
The Academy of Medical Royal Colleges said in a statement: "There is little doubt that things will get worse before they get better."
Prof Stokes-Lampard told Today she had been "profoundly concerned" over restrictions lifting.
Warning of the pressures already faced by medical staff, she added: "It feels in hospitals and GP surgeries as like the middle of winter in terms of how busy we are, rather than July, which would normally see a very low number of infections."
No 10 suggested on Friday that NHS staff could be made exempt from self-isolation if they are 'pinged' by the Covid app in order to help workforce levels.
Prof Stokes-Lampard said it sounded like "a sensible next step".
The latest data published by the Government yesterday showed that a further 35,707 new cases of Covid-19 were recorded in the UK.
It is the highest number of cases recorded in the third wave and since January 23 when there were 33,431 new infections.
Data from the Office of National Statistics' Infection Survey show around 1 in 160 people are testing positive with Covid-19.
