The Delta variant would have “would have ended up in the UK at some point” anyway, even if the borders had been closed sooner, according to an expert in infectious diseases.

Professor Graham Medley from the London School of Hygiene & Tropical Medicine and a member of the Scientific Advisory Group for Emergencies (Sage) advising the Government was speaking to BBC Radio 4’s Today programme.

He warned that it is still possible that the nation could return to seeing hundreds of deaths a day.

He said: “Although the numbers of deaths are low at the moment, everyone expects that they will rise. The question is really as to what level they will rise.

“And at the moment there is a lot of uncertainty in what’s going to happen over the next couple of months.”

Boris Johnson has faced criticism since confirming the government’s decision to delay the lifting of lockdown by an extra four weeks.

Labour accused the Government of “incompetence and indecision” and blamed the delay on border security.

Shadow health secretary Jonathan Ashworth said: “The only reason this delay is being introduced is because the Conservatives failed to secure the country’s borders and a new variant from overseas was allowed to take hold, and failed to put in measures like proper sick pay support and surge vaccinations when needed.”

Asked whether it would have made a difference if Britain had stopped people coming from India in early April, Professor Graham Medley told the Today programme: “Potentially, I mean it’s speculation.

“The newer Delta variant is now quite common around the globe so it would have ended up in the United Kingdom at some point but perhaps it would have been delayed.

“It’s really the competition between the virus and the vaccine so had the variant arrived in the country when we’d had more people vaccinated, then it may well not have grown in the same way that it has.

“It is now the predominant virus in the United Kingdom. And so it got a good start. A lot of cases introduced,

“Whether that’s made a huge difference I think is something that we can look at afterwards but at the moment it’s kind of speculation.”