Dr David Nabarro from the World Health Organisation (WHO) told Sky News “there are going to be more spikes” and some “surges of cases”.
The UK faces a “bumpy ride over the next few months” and the second wave of coronavirus “is coming”, leading health experts have warned.
England’s deputy chief medical officer Professor Jonathan Van-Tam said on Monday a rise in coronavirus cases across the country has come because people have “relaxed too much”.
Dr David Nabarro, the World Health Organisation’s special envoy for the global COVID-19 response, has said “the virus is going to come back” as “life gets going again”.
Asked by Sky News if the country can expect a second wave, he replied: “It’s coming.
“I don’t like it calling it a second wave, I just say there are going to be more spikes and indeed some surges of cases because the virus hasn’t changed.
“It’s the same virus that came and caused so much trouble earlier this year.
“It’s just been lurking, we’ve been very good at holding it back through restricting movement and lockdowns.”
He continued: “Now as life gets going again, younger people are going to university, also there’s some movement around with holidays and of course work – then I’m afraid it does mean the virus is going to come back.”
The UK’s weekly rate of new COVID-19 cases has risen above 20 per 100,000 people – the rate at which it considers imposing quarantine measures on people arriving from abroad.
In the seven days to 7 September, there were 21.3 cases per 100,000, and a total of 14,227.
There were 13.9 per 100,000 in the seven days to 31 August, and a total of 9,259.
There were a further 2,948 lab-confirmed cases of COVID-19 in the UK as of 9 am on Monday, following the 2,988 reported on Sunday, which was the largest daily figure since May.
Professor Van-Tam said the latest coronavirus figures were of “great concern”, adding: “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.”
Asked what is behind the rise in cases, he replied: “People have relaxed too much.”
He added: “Now is the time for us to re-engage and realise that this is a continuing threat to us.”
The deputy chief medical officer for England issued the warning as Caerphilly in south Wales prepared to be placed under local lockdown and stricter measures were extended in Scotland.
It comes as Housing Secretary Robert Jenrick told Sky News there seems to be a rise in the number of cases among young people.
He continued: “Those people… who are out enjoying themselves, who might be going to university this month – they do need to exercise a degree of caution.
“And particularly when they go home and see their elderly relatives.
“It doesn’t mean that they can’t go and meet them, it doesn’t mean that we’re in the kind of restrictions that we were earlier this year.
“But I think it does mean, to exercise that added degree of common sense this autumn.”