There had also been an 80 per cent reduction in COVID-19 hospitalisations following the administration of a first dose.

“That has two points,” Whitty said. “Firstly,these vaccines are highly effective but secondly,they are not completely effective.

“It is absolutely essential that everybody who is called for a second booster dose takes that offer up because it will increase the level of protection and almost certainly the duration of protection as well.”

Whitty said England’s four-month lockdown had helped arrest the number of hospitalisations and deaths but he also credited the effects of the vaccination effort.

Mixing indoors is still banned and indoor dining won’t recommence until mid-May at the earliest. Wales,Scotland and Northern Ireland are also easing their lockdowns in a similar staged way.

A ban on international travel was due to be lifted in May in time for the northern summer holidays,and Johnson said there was “nothing I can see in the data today that would cause us to deviate from the roadmap”.

In one note of caution,modelling conducted for the government’s powerful Scientific Advisory Group on Emergencies warned the full removal of lockdown measures in June could cause a resurgence in hospitalisations to rival the horrific peak of January 2021.

Other scenarios showed a much smaller uptick in hospitalisations.

Johnson has repeatedly said reopening the economy would lead to more cases but has pointed to the vaccination program as the tool to minimise the number of people who fall seriously ill.

The UK is closely monitoring the situation in Chile,which is battling a surge of new infections despite having one of the highest COVID-19 vaccination rates in the world.

“As we get more data,I think the information from other countries as well as our own will tell us how much we can gradually lower our guard,” Whitty said.

“But this is the reason we want to do things in a steady way,because the assumption that you just vaccinate a lot of people and the problem goes away ... well I think Chile is quite a good corrective to that. This is something we’ve got to take steadily.”

Monday marked one year since the Prime Minister was admitted to St Thomas’ Hospital in central London with COVID-19.

The UK’s official death toll stood at 126,862 on Monday.