The Prime Minister insisted a second lockdown was the "last thing anybody wants", but added that the current measures would need to be kept "under review".
According to the European Centre for Disease Prevention and Control (ECDC), Sweden's two-week total of new cases was 22.2 per 100,000 inhabitants on Tuesday.
"There is no doubt, as I have been saying for several weeks now, that we could have expected a second wave and that we are now seeing one coming", the Tory leader said as he visited the construction site of a vaccine center in Didcot, near Oxford.
A Downing Street insider said: "Previously we had to use a mallet as a blunt tool to come down hard on the virus. It's been, I'm afraid, absolutely inevitable that we would see it in this country".
"On Monday we brought in the measures that we did, the rule of six, to restrict what people are doing and to bring in a new buffer".
This week, the government tightened restrictions in the northwest of England, the Midlands and parts of Yorkshire in response to local case spikes.
'We want to avoid a national lockdown but we're prepared to do it if we need to, he told BBC television, vowing to 'do what it takes to protect the public.
The dramatic move was announced as Britain's daily infections hit a four-month high of 4,322, with figures showing the outbreak has almost doubled in size in a week and the R-rate is potentially as high as 1.4.
He said new transmissions are largely taking place in social settings and have already led a doubling in the number of people being hospitalised with the virus every seven to eight days. The R number represents the number of people an infected person will pass the virus on to.
Britain's Office for National Statistics (ONS) confirmed Friday in its weekly infection survey that "the incidence rate for England has increased in recent weeks".
Ministers were on Friday reported to be considering a second national lockdown, after new COVID-19 cases nearly doubled to 6,000 per day, hospital admissions rose and infection rates soared across parts of northern England and London.
The figures do not include people staying in hospitals or care homes.
"We're seeing clear signs this virus is now spreading widely across all age groups and I am particularly anxious by the increase in rates of admission to hospital and intensive care among older people", said Yvonne Doyle, Medical Director at Public Health England.