Whitty said it was a "highly unlikely situation" that the country would be able to ease restrictions earlier than intended, despite positive progress with the vaccination rollout.
"It is highly doubtful that we are going to be in a position where we say the data looks so fantastically better please take more risks here," he said.
Whitty told MPs: "Under all scenarios, if we unlock very suddenly or even significantly faster than is recommended, all the modelling would suggest that we would get a substantial surge while a lot of people are not protected."
While the vaccination policy was substantially reducing the ratio between numbers of infections and deaths among the highest-risk, there has not been as much of an impact on the “actual drive of the wave of transmission, which tends to be in younger adults.”
Whitty said: “They [younger citizens] have not yet been vaccinated and therefore vaccination will have almost no role to play in reducing transmission in that group for some time because we haven't got to that point.
“So if you released [lockdown] very quickly you would suddenly have a wave of transmission in younger adults.”
Whitty warned the committee that “things can go bad very quickly,” and pointed to increasing coronavirus numbers in continental Europe.
The Government’s roadmap sets out five weeks between each stage of easing measures, with confirmation one week prior to moving to the next stage.
The country must meet certain criteria on tackling the virus before being permitted more freedoms.
Within the roadmap, 21 June has been earmarked as the earliest date that all legal limits on social contact can be abolished.
UKHospitality CEO Kate Nicholls reacted to the chief medical officer’s comments on Twitter and said it was “really clear” business support “only provides a route to recovery if dates are maintained.”
The vaccine was always described as our route out of this and it is vital it remains a means to an end. Economically, socially and from a health perspective, there has to be route back through to normality— Kate Nicholls (@UKHospKate) March 9, 2021
She said: “The vaccine was always described as our route out of this and it is vital it remains a means to an end. Economically, socially and from a health perspective, there has to be route back through to normality.”