Asked whether he could guarantee schools will open on January 18, Boris Johnson told the Andrew Marr show: “Well, obviously, we’re going to continue to assess the impact of the Tier 4 measures, the Tier 3 measures.”

On whether GCSE and A-Level exams should be cancelled, the Prime Minister said: “We’ve got to be realistic, we’ve got to be realistic about the pace of which this new variant has spread… we’ve got to be realistic about the impact that it’s having on our NHS… and we’ve got to be humble in the face of this virus.”

Mr Johnson indicated tougher restrictions may be introduced, saying: “It may be that we need to do things in the next few weeks that will be tougher in many parts of the country.

“I’m fully, fully reconciled to that.”

He added: “There are obviously a range of tougher measures that that we would have to consider… I’m not going to speculate now about what they would be, but I’m sure that all our viewers and our listeners will understand what the sort of things… clearly school closures, which we had to do in March is one of those things.”

Boris Johnson said that we must be “humble” in the face of the new Covid-19 variant.

Asked what his message was to councils in England who have said that their schools should close, the Prime Minister said: “My message to such councils is that they should be guided by the public health advice, which at the moment is that schools are safe in those areas where we’re not being driven by the new variant to close them.

“That the priority has got to be children’s education but obviously we want to work with them. I mean we’ve got to be humble in the face of the impact of this new variant of the virus.

“Let’s face it, we face a very difficult few weeks and months until the vaccine comes on-stream.”

Boris Johnson said he hopes lateral flow tests will help with the return of schools.

He said: “We’re going to work with local authorities, work with schools and those responsible up and down the country.

“Our advice remains the same, which is that for public health reasons we think in the large majority of the country, large parts of the country, it is sensible to continue to keep schools open, primary schools, as you know secondary schools coming back a bit later.

“And the second thing is that we are going to be ramping up testing across the whole of the system and I don’t think people have focused enough on this, if I may just for a second.

“One of the things we didn’t have when we went into the first lockdown, where we sadly did have to close schools, was we didn’t have this huge number of lateral flow tests.

“We now have hundreds of millions of lateral flow tests which I believe and hope can be used, deployed, particularly in secondary schools to assist the return of schools.