Some staff at the Treasury had office drinks while England was in lockdown last year.
The Times reported that around two dozen civil servants were present for the drinks on 25 November, 2020.
The group had been working on the Autumn Spending Review, the Treasury said.
It comes after a series of ongoing allegations that COVID-19 rules were broken at parties and drinks in Downing Street in the run-up to last Christmas.
At the time, because of coronavirus regulations, pubs, bars, restaurants, non-essential shops, leisure and entertainment venues were all closed and people were urged to stay at home except for limited reasons including work if it could not be done from home.
Treasury ‘did not organise in-person party’
The Times said Chancellor Rishi Sunak was not at the drinks and it is believed he was not aware of the event at that point.
A Treasury spokesperson said: “In line with the guidance at the time, a number of HMT staff came into the office to work on the Spending Review 2020.
“We have been made aware that a small number of those staff had impromptu drinks around their desks after the event.
“The Treasury did not organise an in-person departmental party last Christmas.”
Sky News understands the drinks were brought in by the staff themselves and were not provided by the Treasury.
There are ‘pictures from parties’
It comes as the prime minister’s former chief adviser has said there are pictures from parties in Downing Street during strict COVID restrictions that will “inevitably get out” – as two polls showed the Tories being overtaken by Labour.
Dominic Cummings, who left Number 10 last November, made the claim about the images on his Twitter account.
Government chief whip Mark Spencer has insisted Downing Street staff “were not drinking alcohol” and partying during lockdown after revelations the prime minister’s press chief addressed staff at one event last Christmas.
Adviser ‘handed out awards’
Boris Johnson‘s most senior communications adviser Jack Doyle handed out awards on the night of the alleged Downing Street party last year during a time of strict COVID restrictions, it is understood.
Mr Doyle, the director of communications at Number 10, thanked staff working there “like he does every week”, a spokesperson said.