Coronavirus cases, hospital admissions and deaths from the disease are increasing across the UK, as decision day looms for the government to further relax restrictions.
But the country's vaccination programme means large sections of the population have received at least one dose.
Countries across Europe have reported a rise in cases, including in France, where the Delta variant is now the dominant strain, and the Netherlands, where authorities have reimposed lockdown restrictions.
Medical leaders in the UK, including the Academy of Medical Royal Colleges, said Covid-19 cases were about to “rise dramatically” and that the outbreak would become worse before it got better.
The government has said it is ready to ease most restrictions in England, but a final decision will not be made until Monday, with the order to take effect on July 19.
Among the rule changes expected to be confirmed is the removal of the legal requirement for masks to be worn in many public places.
But UK Vaccines Minister Nadhim Zahawi said on Sunday that there was "an expectation of people to wear masks indoors, in crowded places and on public transport".
Asked by the BBC if this represented a change in policy, he said: "We're moving from 'you must' to 'you are expected' to wear a mask in indoor spaces."
On Saturday, UK authorities reported 32,367 new cases and 34 deaths in the previous 24 hours.
That case tally was slightly down on the previous day, but in the past week the number of infections has increased by about 31 per cent and deaths rose by about 43 per cent.
The number of hospital admissions was 509 on July 5, the latest data available showed.
In the seven days leading up to July 5, there was a rise of almost 56 per cent in hospital admissions – 2,872 cases – compared with the previous week.
The academy said the country's National Health Service was “under unprecedented pressure” and gave a warning against dispensing with safety precautions when restrictions were eased.
“There seems to be a misapprehension that life will return to normal from then and that we can throw away all the precautions and, frankly, that would be dangerous,” academy chairwoman Prof Helen Stokes-Lampard said.
The academy, which represents 23 medical groups, said there was “little doubt that things will get worse before they get better".
“There is no doubt that we will get to a position when this dangerous and erratic disease is largely under control for the population as a whole and we can 'learn to live with' Covid-19,” it said.
“However, we are not in that position yet and, sadly, we have to expect things to get worse again.”
UK Prime Minister Boris Johnson said that assuming restrictions were lifted on July 19, the country could record a mass outbreak of 50,000 infections a day.