UK vaccines minister Nadhim Zahawi said scientists are looking at a range of options for the booster, including new vaccines altered to cope with variants, or mixing the type of injection on offer.
It comes as Scotland nears the target of having given a first dose to all over-50s and those with underlying health conditions.
The Scottish Government has previously said a rollout of booster vaccines in the autumn is likely, especially for those most vulnerable.
Mr Zahawi said England’s deputy chief medical officer Professor Jonathan Van-Tam is conducting a clinical trial to look at “which vaccine delivers the best boost”.
He told Sky News on Wednesday: “We want them to be able, if they need to, from September onwards to boost those that are most vulnerable.”
UK Health Secretary Matt Hancock said testing facilities at Porton Down in Wiltshire are to be bolstered to help “future-proof” the country, with a £29.3 million boost confirmed for the expansion of the laboratories where scientists test existing and new vaccines against variants of concern.
The Government has ordered 60 million doses of the Pfizer vaccine in preparation for a booster campaign. 100 million doses of vaccine have also been ordered from Valneva, which is manufacturing its vaccine in Livingston.
Mr Zahawi said: “Pfizer is one option, we’re going to give them an AstraZeneca option, we’re working with the team on a vaccine variant.
“Clinicians haven’t yet made the decision when they will need to boost, whether to give more immunity to the most vulnerable, to increase the durability of the protection or to deal with the variant.“When they decide, I want to give them as much optionality, as many vaccines that were, then they will make those choices.”
Mr Zahawi told BBC Breakfast the investment into Porton Down would “future-proof the vaccination programme for next year and the years beyond that, as we move from pandemic to endemic and deal with it in the way we would deal with the annual flu vaccination programme”.
Asked whether all over-50s will be offered a booster shot before winter, Mr Zahawi said “that decision hasn’t been made”.