Professor Sir John Bell, an Oxford academic and member of the government’s Scientific Advisory Group for Emergencies, said he had “no concerns” over the candidate, which is still being reviewed by the UK’s Medicines and Healthcare products Regulatory Agency.
Approval of the vaccine would be a major boost to efforts to control Covid-19 as it is easier to distribute than the Pfizer/BioNTech jab currently being used in the UK.
The government has ordered 100 million doses of the Oxford/AstraZeneca vaccine, with around 40 million due to be available by the end of March.
Sir John, Oxford University's regius professor of medicine, told BBC Radio 4's Today programme that he expects MHRA approval "pretty shortly".
"They got data quite a long time ago but that was the first set of data,” he said. "They receive multiple sets of data.
"So we are getting to be about prime time now, I would expect some news pretty shortly.
"I doubt we'll make Christmas now, but just after Christmas I would expect.
"I have no concerns whatsoever that the data looks better than ever."
Data released last week from phase one and two clinical trials for the vaccine confirmed that it stimulates a broad range of antibody and T-cell responses in people.
Findings from phase three trials published in The Lancet earlier this month also reiterated that the jab is 90 per cent efficacious if administered at a half dose and then at a full dose, or 62 per cent effective if administered in two full doses.
The MHRA is conducting a rolling review of the candidate and will make a decision on which dosage regime to authorise for market use.
Last week, Jeremy Hunt, the former Tory health secretary, said approval of the Oxford vaccine would allow the UK to step up its vaccination programme.
"It will make a massive difference because the doses we have of the Pfizer vaccine will keep us going until the end of January,” he said.
"I think we’re not getting another shipment until March.
"So if we get that Oxford/AstraZeneca vaccine ready to go in January then we can keep the roll out going at its current pace."
Former prime minister Tony Blair has meanwhile called on the UK’s vaccination plan to be “altered and radically accelerated” in response to the emerging threat posed by the new variant of coronavirus.
Writing for The Independent, he urged decision makers to speed up approval of new vaccines, including the Oxford jab.
And while patients will require two jabs to be fully protected, Mr Blair urged Downing Street leaders to use up all of the first batch of the Oxford-AstraZeneca vaccine next month while a second round is produced.
The former Labour leader said the first dose would still provide “substantial immunity” and that full effectiveness could follow “a second dose two to three months later – longer than originally thought”.
The former premier also criticised the "somewhat inflexible 'by age' structure" used to determine who receives the jab.
Experts at the Joint Committee on Vaccination and Immunisation have drawn up a priority list based on clinical need.
But Mr Blair, who does not have a medical background, said "there is a strong case for saying you have got to focus also on the people spreading the disease, not simply the most vulnerable".
Communities secretary Robert Jenrick told the BBC that the government is focusing on getting as many people as possible to receive the first dose of the Pfizer vaccine.
"At the moment the priority is just to ensure that as many people as possible get the first shot of the vaccine," he said.
"Remember, the second shot has to be done, depending on what the vaccine is, 21 or 28 days later and so we still haven't reached that point with the first people who were vaccinated."
Additional reporting by PA