England’s chief medical officer Chris Whitty has warned that the UK’s Covid pandemic could “turn bad very fast” again if Boris Johnson caves to Tory MPs’ demands to accelerate the route out of lockdown.

In evidence to MPs, Whitty said that those who think that the vaccination programme is a “get out of jail” card have failed to grasp that younger people – who are not yet jabbed – are the main driver for transmission of the virus.

He also predicted that even with a successful vaccination rollout to all age groups, there was likely to be a new “surge” of Covid this year, either gradually in “late summer” or in the autumn.

Speaking to Commons science and technology committee, Whitty warned against moves to “concertina up” the gaps between relaxation of restrictions in the PM’s roadmap out of lockdown, saying five weeks remained the minimum period needed to react to the impact of each stage.

The chief medical officer hit back at calls by some MPs for a fast-tracking of the roadmap, under which restrictions are changed in stages before all curbs are largely lifted on June 21.

“People should remember that things can turn bad very fast if you don’t keep a very close eye on what’s going on,” he said. “If you open up too fast, a lot more people die.”

Referring to the vaccination programme, he added: “The idea that is a sort of ‘get out of jail’ card, in terms of a surge of transmission, I think is to misremember where in the age spectrum the drive of transmission is – and it’s in younger adults.

“Look at what is happening in continental Europe at the moment where a lot of countries are going back into rates going up and having to close things down again.”

And Whitty had a stark assessment of the way the pandemic had unfolded in the UK and the rest of the globe.

“If you look at the history of this all around the world, the history of this is not full of countries and individual leaders wishing they had [lifted lockdown] fast[er]. It’s full of leaders who wish they had actually [imposed lockdown] quicker, and then been more careful as they take things off.”

Whitty also stressed that each of the stages in Johnson’s roadmap contained “large blocks of potential risk”, because each included multiple changes to daily life.

The April 12 measures, when shops and outdoor hospitality are due to open, were “a very big block”. May 17 “is a very significant block with a lot of stuff that is indoors for the first time – that is the point when we are really going to start to see some very significant risks accumulating, potentially”.

Asked whether the government’s message of “data, not dates” was just a slogan, chief scientific adviser Sir Patrick Vallance said “for us it is not”.

He said “take off from this point can lead to quite high numbers very quickly”.

Whitty said that even if the vaccines were 99% effective and even if take-up was higher, there would still be a real risk to the public. Just as flu claims lives every year, modelling suggested there could be around 30,000 deaths from Covid later this year.

“What we are going to see is, as things are opening up, what all the modelling suggests is that at some point we will get a surge in virus,” he said.

“We hope it doesn’t happen soon – it might, for example, happen later in the summer if we open up gradually, or because of the seasonal effect it might happen over the next autumn and winter.

“All the modelling suggests there is going to be a further surge and that will find the people who either have not been vaccinated or where the vaccine has not worked. Some of them will end up in hospital and sadly some of them will go on to die.”