Deputy prime minister Dominic Raab has been unable to guarantee that all adults who want their booster by the end of the month will be able to get it.
The justice secretary said the government was doing “everything we can” to get people jabbed as swiftly as possible.
But he opened the door to confusion as to whether that was an offer or whether people would actually receive their jab by the end of December.
On Sunday night Boris Johnson announced a new deadline of jabbing everyone over 18 by the new year in a bid to tackle the variant, prompting a mad rush on vaccine centres and on booking sites.
The following day the prime minister’s official spokesman also clarified that if those eligible booked in time, it was the actual jab – not just an appointment – that would be met by the end of December.
Following reports of chaos, Sky News’ Kay Burley asked: “Will everybody who wants one be able to get a jab by December 31?
“It’s a yes or no question.”
Raab replied: “We are doing everything to get as many people as we possibly can jabbed, and of course, we’re starting from now — I think it’s 41% who have had the booster.
“We’ve got that capacity, we’re ramping it up and we want to get as close to that as possible, but the offer is, the target is to get everyone over 18 offered to have that booster.”
Burley interjected: “But no guarantee?”
Raab replied: “We’ll do everything we can, we’re straining every sinew.”
The emphasis on the booster programme comes amid warnings that omicron will soon replace Delta as the dominant variant in the UK.
Scientists believe it is already causing up to 200,000 infections a day.
On Monday the prime minister confirmed there had been at least one death with omicron.
The justice secretary also mixed up figures around how many patients had been hospitalised with omicron, originally saying it was in the low hundreds before revising that down to nine.
It is understood that the correct figure for those in hospital with the omicron variant is 10.