The UK R number, which represents the number of people an infected person will pass the virus to, has risen to between 1.1 and 1.4, meaning cases can rise very quickly, according to Sage.
Public Health England (PHE) warned that data published on Friday could be a sign of “far worse things to come”, as the Office for National Statistics (ONS) said cases are thought to have almost doubled in a week to 6,000-a-day in England.
Speaking to reporters on Friday, the Prime Minister said it was “inevitable” that coronavirus would hit the country again.
During a visit to the Vaccines Manufacturing Innovation Centre construction site near Oxford, Mr Johnson told broadcasters: “Obviously, we’re looking very carefully at the spread of the pandemic as it evolves over the last few days and there’s no question, as I’ve said for several weeks now, that we could expect (and) are now seeing a second wave coming in.
“We are seeing it in France, in Spain, across Europe – it has been absolutely, I’m afraid, inevitable we were going to see it in this country.”
He said a second lockdown was the “last thing anybody wants” but said the current measures would need to be kept “under review”.
“On Monday we brought in the measures that we did, the ‘rule of six’, to really try and restrict what people are doing and to bring in a new buffer – and to make it absolutely clear, the ‘rule of six’: indoors six maximum, six outdoors maximum," said Mr Johnson.
“But the crucial thing is at the same time to observe the basic rules on social distancing – hands, face, space – that is what everybody has got to do if we want to continue to beat this thing.
“But as we look at this particular curve and what is happening now, clearly we are going to keep everything under review. I don’t want to get into a second national lockdown at all, it is the last thing anybody wants.
“I don’t want to go into bigger lockdown measures at all, we want to keep schools open and it is fantastic the schools have gone back in the way they have. We want to keep the economy open as far as we possibly can, we want to keep businesses going
“The only way we can do that is obviously if people follow the guidance.”
The Prime Minister said his administration was considering whether it needed to “go further” than the current national restrictions that were put in place this week.
Asked about the possibility of a two-week October half-term in order to bring in a short lockdown, Mr Johnson told reporters: “What I can certainly say about parents and schools is we want to keep the schools open, that is going to happen.
“We want to try and keep all parts of the economy open as far as we possibly can – I don’t think anybody wants to go into a second lockdown but clearly when you look at what is happening, you have got to wonder whether we need to go further than the ‘rule of six’ that we have brought in on Monday, so we will be looking at the local lockdowns we have got in large parts of the country now, looking at what we can do to intensify things that help bring the rate of infection down there, but also looking at other measures as well.
“What I will say is, as we go forward, we will be explaining in great detail to people what the scientific background is, what the epidemiology is saying and really how we propose to do it.”
When asked if the Government had eased lockdown too quickly, Mr Johnson suggested discipline in adhering to social distancing restrictions had slipped.
He said: “If you look at what’s happened over the last few months, I think the British people have done a amazing job.
“They got that peak under control, they brought it right down, they brought the number of infections right down by discipline and everybody adjusting our behaviours and the way we go about our lives – hands, face, space.
“And I think probably, truth to tell, what’s happened here and what alas has happened in so many other countries is that people find it difficult to keep this up.
“It is very difficult to maintain that kind of discipline for a long time and what you’ve seen is the disease starting to spread again among young people and that’s where it really started to kick off in France and Spain in those age groups and we are now seeing that here in this country.”
Nicola Sturgeon and Labour leader Sir Keir Starmer also backed Mr Khan's calls for an emergency meeting. Cobra is shorthand for the Civil Contingencies Committee, meeting involves a cross-departmental committee that comes together to respond to national emergencies.
This is the time for swift, decisive national action. We cannot afford to be too slow.
That’s why I’m asking the Prime Minister to convene a COBRA meeting and to update the country on the measures the Government‘s taking to keep the virus under control, including to fix testing.— Keir Starmer (@Keir_Starmer)September 18, 2020
Meanwhile Health Secretary Matt Hancock said a second national lockdown to curb the spread of coronavirus has not been ruled out, but the “great hope” is that people will heed current advice to help manage a “very serious” situation.
He said a national lockdown is the “last line of defence”, as he responded to reports that ministers are considering further national measures, even for just a two-week period, such as imposing a curfew on bars and restaurants.
Mr Hancock told BBC Breakfast it was “absolutely critical” people followed the rules, adding: “If we do all these things, then we can avoid having to take serious further measures.”
He added: “We want to avoid a national lockdown but we’re prepared to do it, if we need to.”
On Friday, new confirmed daily cases of coronavirus hit 4,322 – the highest since May 8.
Cases of the virus and hospital admissions for Covid-19 are doubling every seven to eight days in the UK, according to the new data.
Yvonne Doyle, medical director at PHE, said: “We’re seeing clear signs this virus is now spreading widely across all age groups and I am particularly worried by the increase in rates of admission to hospital and intensive care among older people.
“This could be a warning of far worse things to come.”
Additional reporting by PA Media.