Sajid Javid, the Health Secretary, told the Commons he wanted to “put the booster programme on steroids because that will really help us”.

He said the moves were “a huge step up for our vaccination programme, almost doubling the number of people who will be able to get a booster dose to protect themselves and their loved ones”.

But on Monday, NHS officials were unable to say when the rules would even take effect. Officials insisted that anyone who had waited more than three months since their second dose should wait to be contacted.

People would continue to be prioritised in age order, they said.

Booking opened up to those in their 40s last week, under rules which insisted on a six-month gap between doses. The change in the interval to three months should speed up the rollout and ensure those aged 40 and over get their third jabs before Christmas.

However, it is unclear how many younger people will be offered jabs this year. 

At the height of the rollout last spring, the programme was administering around 3.5 million jabs a week. But since then the rollout has been scaled back, with about 50 mass vaccination centres closing and many GPs dropping out of the programme.

Prof Van Tam said on Monday: “I think the important message that the NHS wanted me to convey to you today is that they understand the real urgency of this. 

“They are up for the task, but they say that they will contact you when you need to act. And they will open the booking in any orderly way, because one of the things we really don’t want is people from the very youngest now eligible cohorts somehow getting in front of people who are much, much higher risk of a bad outcome if they were to get Covid-19.”