People scheduled for a booster jab who refuse it may be blocked from quarantine-free overseas travel.
Ministers have discussed plans to reinstate quarantine and testing for travellers who refuse to take the booster jab.
“This is not going to happen immediately – but happen it will,” a government official said.
The government hasn’t decided when to implement it and could allow a grace period for people to travel without quarantine if they have booked a booster jab but are still awaiting an appointment.
“Almost 10 million people in the UK have received their Covid-19 booster and third jabs, a phenomenal achievement in under two months,” Health Secretary Sajid Javid said.
“As we approach this milestone, I want to thank those who have come forward and urge everybody across the nation to get vaccinated, get protected and get boosted.”
Meanwhile, the NHS app needs to be updated to allow a third jab to be uploaded and verified.
Currently, the app doesn’t recognise a third vaccine dose.
Countries including Israel and Austria are imposing six-month expiry dates on double doses.