Boris Johnson has refused to guarantee that this will be Britain’s final Covid lockdown – just minutes after saying the opposite.

The prime minister said in a broadcast interview on Monday that he would lift restrictions in a way that was “cautious but irreversible”, a line he repeated at the daily coronavirus press conference. 

But at the same press conference minutes later, he appeared to perform a U-turn.  

Asked if he could commit to the UK’s third lockdown being its last, he said: “No, I can’t give that guarantee, of course not, because we’re battling with nature, with a disease that is capable of mutating and changing.”

His words are likely to enrage Conservative Party backbench faction the Covid Recovery Group, which is pressuring the government to lift restrictions by the end of April. 

It came as the government raised hopes an unlock plan could be moved forward on Sunday when it was revealed that more than 15m people had now had their first jab – the size of the top four vulnerable groups. 

Johnson said the vaccination programme continued to “power past” the targets set for it but warned now was not the time to ease up on efforts to tackle the virus.

“This is an unprecedented national achievement but it is no moment to relax,” he said. 

“In fact it is the moment to accelerate because the threat from this virus remains very real.”

Although more than 90% of over-70s had been vaccinated, some 60% of hospital patients with Covid-19 were under that age.

Johnson’s repeated reference to an “irreversible” unlocking of Britain echoes the words of health secretary Matt Hancock, who told MPs on the Commons health committee last month that he could foresee this being the UK’s final lockdown thanks to the vaccination programme.