Further restrictions to social and economic life are due to be relaxed on Monday, with the majority of curbs lifted altogether in June, allowing the public to gather inside with no limits for the first time since the onset of the pandemic.
But there are concerns over the rise in infections with the so-called Indian variant of coronavirus, particularly in the Greater Manchester area.
Speaking during a visit to a school in County Durham, Mr Johnson said: “We are anxious about – it has been spreading.”
The prime minister said there would be meetings later on Thursday to discuss what to do, and that he was “ruling nothing out” when asked if local lockdowns were possible.
“There are a range of things we could do, we want to make sure we grip it,” he said. “Obviously there’s surge testing, there’s surge tracing.
But he added: “At the moment I can see nothing that dissuades me from thinking we’ll be able to go ahead on Monday and indeed on 21 June, everywhere, but there may be things we have to do locally and we will not hesitate to do them if that is the advice we get”.
His remarks come as experts on the Scientific Advisory Group for Emergencies (Sage) were called to an urgent meeting to assess the threat of the the variant — B1617.2 — which is one of three mutations causing the spike in Covid infections in India.
It was reported there are concerns among scientists that while England’s next stage of the roadmap on Monday will go ahead, with people allowed to meet inside in groups of six, the fourth and final step out of restrictions on 21 June could be delayed.
According to official government figures — due to be updated on Thursday — 520 cases of the B1617.2 variant have been have been confirmed by officials tracking the data.
Health officials have designated all three of the Indian Covid variants – known as B1617.1, B1617.2 and B1617.3 – as “under investigation”.
Mr Johnson told reporters: “It’s a variant of concern, we are anxious about it. At the moment there is a very wide range of scientific opinion about what could happen.
“We want to make sure we take all the prudential, cautious steps now that we could take, so there are meetings going on today to consider exactly what we need to do. There is a range of things we could do, we are ruling nothing out.”