Boris Johnson warned there is always the possibility of a new variant derailing the unlocking process after he postponed the final stage of unlocking last night.

The June 21 date for the final lifting of coronavirus restrictions was delayed until July 19 last night after concerns about surging cases of the Delta variant.

However, Mr Johnson said he is confident we will not need to go beyond four weeks’ worth of delays.

“At a certain stage, we are going to have to learn to live with the virus and to manage it as best we can,” he said.

“What we are trying to do now, by this delay, is to reduce the current surge and we think we can do that.

“We think a two-week delay would make a substantial difference and a four-week delay would make even more of a difference in reducing the overall number of deaths.”

By July 19 there will be a “very considerable wall of immunity around the whole of the population.

“At that stage, on the basis of the evidence that I can see now, I’m confident we will be able to go forward with the full Step four, the full opening.”

But he added: “That, of course, does not exclude the possibility – I’m afraid, and we have got to be honest about this – the possibility that there is some new variant that is far more dangerous, that kills people in a way that we currently cannot foresee or understand.”

In more promising news, last night’s announcement comes after research from Public Health England suggested the two Covid vaccines most in use in the UK are "highly effective" in preventing hospital admission with the Delta variant.

The Pfizer-BioNTech vaccine was found to be 94 per cent effective against hospital admission with the Delta variant after just one dose, and 96 per cent after two doses.

The Oxford-AstraZeneca vaccine was found to be 71 per cent effective against hospital admission after one dose, and 92 per cent after two doses.

PHE says the protection against death is expected to be high, although further research is taking place.

Mr Johnson confirmed 23 and 24-year-olds will be able to book their vaccine today.