Plans to scrap PCR tests for most people coming into the country leaves the UK "flying blind as the pandemic rages", a top scientist has warned.
The government's proposals to ditch the tests for double-vaccinated arrivals have been strongly criticised by Richard Horton, editor-in-chief of the medical journal the Lancet.
He has warned that the UK is "one a knife's edge" in its pandemic response, and making a wrong move now could be disastrous.
The fellow of the Royal College of Physicians has said that a new, potentially deadlier variant could get into the country if testing for travellers is largely ditched and the UK does not play its part in the global vaccine effort.
Dr Horton has also lambasted the government's plans to offer booster shots to over-50s and the vulnerable, which he says is not guided by the science and will use up valuable vaccines that could be put to better use elsewhere.
"I am very concerned that the government is planning to lift as many of the restrictions as they seem to be trailing," he told The Mirror.
"I am also very worried about the plans for a booster vaccine campaign. I don't think this is being guided by the science at all.
"There is no evidence that we need boosting in the general population, there is no evidence of declining effectiveness against severe disease in the general population.
"Boosting could be appropriate for people who have compromised immune systems, but it is not necessary in the general population including the elderly.
"We need to be putting vaccines where they can do the most good, in the completely unvaccinated that are driving transmission worldwide."
Dr Horton went on to describe plans to ditch PCR tests for double-jabbed travellers, as Health Secretary Sajid Javid says he wants to do as "soon as I possibly can", as "totally crazy".
He urged the government to boost testing capacity and reach those who haven't been vaccinated, including teenagers.
"We let Delta in because we didn't have good border controls," he continued.
"The only way to detect variants is taking samples through PCR tests, if we don't detect variants we are at risk of being overrun by a new one.
"We are flying blind as the pandemic rages globally. The lesson is, if you look at every country, their failures have been because they did too little too late.
"The UK has the second highest number of new infections in the world at the moment. That means that although our vaccine campaign has been very successful, the fire is still burning.
"The number of hospitalisations are slowly creeping up. It's now 1,000 deaths a week. We're on the edge.
"We need to accelerate vaccination and we need strong public health messaging telling people to continue wearing masks, work from home and socially distance.
"If we take our foot off the gas in terms of jabs and testing, we will fall off the edge. We're going into the winter and we could find ourselves, with Covid and influenza, in the perfect storm".
Later this week Boris Johnson is expected to announce booster jabs for the vulnerable and older people, as well as an expansion of the vaccination programme for 12 to 15-year-olds.
The government hopes that the vaccine rollout means that the country will not need to be put in another lockdown.
David Matthews, professor of virology at the university of Bristol, largely backs the government's proposals.
He has said that the "spectacular success" of the vaccine means the country is in a good place before expressing hope that it will stop a further lockdown being needed.
However, Professor Matthews criticised the scrapping of planned vaccine passports which he argued would help convince the final five million unvaccinated adults to get the jab.
"I am not sure that I agree that it is someone's personal freedom to needlessly occupy a hospital bed in the place of someone else whose need is greater," he told The Mirror.
"I don't perceive that as someone's personal right. People think that it won't happen to them, but at the same time, why do we all wear seatbelts?"
Professor Neil Ferguson, whose modelling was instrumental to the UK going into lockdown in March 2020, said experts were seeing "slow increases in case numbers, hospitalisations and deaths".
The scientist, from Imperial College London, and a member of the Scientific Advisory Group for Emergencies (Sage), told BBC Radio 4's Today programme that in the absence of social distancing measures, which he did agree with, "we are reliant on immunity building up in the population".
Professor Ferguson also told BBC Radio 4's Today programme that vaccinating teenagers was the priority.
However, he was supportive of booster jabs for a wider population, saying that evidence from Israel suggests they "really are very effective at further driving down transmission and infection".
Asked whether a further lockdown could be ruled out, he said "I hope so" but added that "you can't rule out anything completely."
He said he was pleased to see things like the ability to ask people to work from home could be retained in the Government's forthcoming winter plan for tackling Covid-19.
He suggested there could be a small effect from ditching Covid passports on the spread of the virus "but it won't be huge".
