UK Edition
The public "relaxed too much" following the easing of lockdown restrictions, according to England's deputy chief medical officer, who described the recent surge of coronavirus cases as a "great concern".
The country will have a "bumpy ride" in the coming months if infection rates are not brought under control, Professor Jonathan Van Tam warned on Monday night.
He suggested coronavirus is not being confined to certain areas, saying a "general creeping geographic trend across the UK" is being observed.
The seven-day rate of new cases of Covid-19 in Britain has risen above 20 cases per 100,000 people – above the Government threshold which triggers quarantine from other countries.
On Sunday, 2,988 new cases were announced, the highest increase since May 22. A further 2,948 cases were recorded on Monday (use the tool below to find out about virus cases in your local area).
"This is a virus we're going to have to live with – and if we're not careful, if we don't take this incredibly seriously from this point in, we're going to have a bumpy ride over the next few months," Prof Van Tam said.
"Now is the time for us to re-engage, and to realise that this is a continuing threat to us."
Younger people are "potent spreaders" infecting the elderly, he said, adding: "Where case numbers rise initially in the younger parts of the population, they do in turn filter through and start to give elevated rates of disease and hospital admissions in the older age groups, and we know that then becomes a serious public health problem.
"The fact that 17 to 21-year-olds are not becoming ill means they are lucky, but they also forget, because the disease is not severe for them, that they are potent spreaders."
He added that hospital admissions and deaths in the UK were currently at "a very low level".
Britain's soaring cases raise the prospect that other nations could add the country to their travel quarantine lists.
When other countries reach a rate of 20 cases per 100,000 or above, the UK Government considers imposing quarantine conditions on people travelling to Britain.
The threshold has seen holidaymakers returning from France, Croatia, Spain and other countries forced to self-isolate for 14 days on their return.
From 4am on Wednesday, seven Greek islands will be added to Britain’s quarantine list, with those returning from Lesvos, Tinos, Serifos, Mykonos, Crete, Santorini and Zakynthos (also known as Zante) losing their exemptions from the UK's travel corridor.
However, every country runs its own surveillance system and sets its own thresholds, meaning no changes are automatic.
Nearly 6,000 new confirmed cases of Covid-19 have been reported in the UK in the 48 hours to 9am on Monday, with the daily rate now 50 per cent higher than it was before the weekend.
The latest weekly statistics show almost one third of infections in England are among those in their 20s, with more than 2,000 cases among those aged between 20 and 29.
Matt Hancock, the Health Secretary, said on Monday that while earlier rises in the spread of the virus had been linked to poorer areas, the latest rises appeared to be driven by wealthier young people.
He said: "Over the summer we had particular problems in some of the areas that are most deprived. The recent increase we have seen in the last few days is more broadly spread. It's actually among more affluent younger people where we have seen the rise."
In a message to younger people on BBC Newsbeat, he said: "The question is, how much are you willing to risk the lives of yourself and others by breaking the social distancing rules? Don't kill your gran by catching coronavirus and then passing it on."
There is concern that socialising over the August Bank Holiday weekend, in house parties and bars, is only now being seen in infection rates, which could translate into rising increased hospital admissions in weeks.
Mr Hancock pointed out that the second waves being seen in Spain and France "started largely among younger people".
"In Spain the number of hospitalisations has gone up by 14 times since the middle of July. In France, the number of people in hospital has trebled over the last month or so," he said.
Asked by LBC presenter Nick Ferrari whether the UK had "lost control", as suggested by some doctors, Mr Hancock said: "No, but the whole country needs to follow social distancing. We certainly see cases where if they are not, then we take action.
"For example in Bolton, where numbers are the highest, we traced a lot of those cases back to an individual pub and we have taken action on that pub. The pub needed to close and sort the problem out."
Mr Hancock said the most important point to get across was that the uptick in cases in the past few days had been in younger people under 25, "especially 17 to 21-year-olds".
Dr Yvonne Doyle, the medical director and director of health protection at Public Health England, said: "What we don't want to see is a continuing increase of cases in this age group because it could lead to them infecting their parents and grandparents, who are much more at risk of poor outcomes from the virus.
"It is vital that they follow social distancing rules, wash their hands regularly and wear a face covering in enclosed spaces."
Professor Carl Heneghan, the director of the University of Oxford's Centre for Evidence-Based Medicine, said there "is currently no second wave" (see graphic below).
He added: "What we are seeing is a sharp rise in the number of healthy people who are carrying the virus, but exhibiting no symptoms. Almost all of them are young. They are being spotted because – finally – a comprehensive system of national test and trace is in place."
Overall, data from Public Health England for the seven days to September 4 shows that Bolton has the highest rates in the country. The rate of 121.7 cases per 100,000 people is up sharply from 48.3 in the seven days to August 28.
Levels in Bradford have risen from 46.3 to 70.6, while Blackburn with Darwen, where the rate has risen from 47.4 to 62.8, is in third place.
Significant rises were also seen in Birmingham, Leeds and Liverpool.