Boris Johnson said tonight that although he could not guarantee there would be no further lockdowns across the UK, he stressed that “science is now unquestionably in the ascendancy over the disease”.

And he said he was “increasingly optimistic about the sheer extent of the possibilities that are opening up with vaccinations”.

NHS England boss Sir Simon Stevens said it was hoped all over 50s, as well as others in the first nine priority groups, would be offered a vaccine by April 30.

And Mr Johnson said the vaccination programme “continues to power past the target we set six weeks ago”.

But speaking from Downing Street, after the milestone of delivering 15m vaccines was passed, Mr Johnson said: “This is an unprecedented national achievement but it’s no moment to relax and in fact it’s the moment to accelerate because the threat from this virus remains very real.”

The successful rollout of the vaccine programme is leading to increased pressure from the Covid Recovery Group (CRG) of Conservative MPs to end restrictions quickly.

Over the weekend, more than 60 CRG members signed a letter calling for the Prime Minister to commit to a firm timetable ending with the lifting of all legal controls by the end of April.

Chief Medical Officer for England Professor Chris Whitty said although hospitalisations and deaths from coronavirus were falling, the country was only now reaching the infection rates of what was the peak of the outbreak in April last year.

“They [rates] are around the point, in fact slightly above the point, which they were at the peak of the epidemic in April last year,” he told the press conference. “So these are still very high rates but they are definitely heading in the right direction.”

A further 230 deaths were recorded yesterday in the UK within 28 days of a positive Covid test, bringing the country’s total to 117,396.

Sir Simon said the end of April had been set as the target to vaccinate the top nine priority groups due to “likely vaccine supply” but added that “if supply increases then we think we can go faster”.

While Mr Johnson is due to set out his plan to unlock the country on February 22, likely to begin with children returning to the classroom, but he said the public must “be both optimistic but also patient”.

He added: “Because we want this lockdown to be the last, and we want progress to be cautious but also irreversible.”

He said: “We don’t really yet have sufficient clarity on the data to be sure now, today, as of this Monday 15 exactly what we’ll be able to say to you on Monday 22.

“That’s because the data becomes clearer with every day that passes and we have to continue to evaluate. And also, to be absolutely clear, these decisions we will take in the course of this week but they are not yet taken.”

Millions more to be vaccinated by end of April as PM warns country to be 'optimistic but also patient' over lockdown lifting