Health Secretary Sajid Javid insists people will have access to Covid-19 booster injections from next month.
Mr Javid could not say exactly when the third doses would be rolled out but is “confident” it will start “sometime” in September.
Experts are awaiting more trial results but the NHS has already planned to be ready for September 6.
Today the Joint Committee on Vaccination and Immunisation discussed who should get a third jab but an announcement is still likely to be weeks away.
Vaccinations are estimated to have saved between 91,700 and 98,700 deaths, says Public Health England.
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Its latest figures are up on a previous estimate of between 81,300 and 87,800 deaths.
PHE, working with Cambridge University, also calculated the inoculations had prevented 82,100 hospital admissions and from 23.6 million to 24.4 million infections.
A source said of the booster rollout: “The jury is still very much out on what happens. We have found when we undertake clinical trials, the results can be surprising.”
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In June the JCVI said there may be two stages to a rollout, similar to the rules for first doses.
Other countries which vaccinated their populations early such as Israel have already given booster jabs to the general population.
US President Joe Biden has said third shots will be offered to all Americans from September 20.
JCVI member Professor Adam Finn, of Bristol University, said: “There will be some people who will need a third dose, particularly people who we know are very unlikely to be well protected by those first two doses.”
Those with underlying health conditions and whose immune systems are compromised may get them first.
Prof Finn said: “We need to focus on individuals who are more likely to get sick again if they have not got a booster.”
Research from Oxford University has revealed a drop off in protection from the Pfizer jab after four months.
It also found a minority of people who still catch the Delta variant are just as likely to develop symptoms and spread the virus as the non-jabbed.
Prof Finn added that the vaccination programme had not been as good as they had hoped at stopping the virus from circulating.
Yesterday the number of UK Covid cases was 6,392,160, up 36,572, and deaths were 131,373, up 113.
Prof Peter Openshaw, of the New and Emerging Respiratory Virus Threats Advisory Group, which advises the Sage group, said high case numbers and deaths are concerning.
He said: “I think it’s very worrying. This is a very large number. To be seeing over 100 deaths a day at this stage, before schools have gone back, while the weather is still relatively good, we’re not back into winter yet.”
The NHS has launched a new drive to vaccinate all 16 and 17-year-olds before their return to classrooms.
Letters were received yesterday and follow-up text messages will be sent out inviting teens for appointments at local walk-in centres.
Mr Javid said: “I urge you to join the hundreds of thousands of 16 and 17-year-olds who have already taken up the offer of vaccine as quickly as possible to ensure you get vital protection before returning to college or sixth form.”
