British Prime Minister Boris Johnson's press chief gave out joke awards and made a thank you speech at a Downing Street party on December 18 last year while London was under strict lockdown, according to CNN affiliate ITV.

Jack Doyle, who was Johnson's deputy director of communications at the time, addressed a gathering of "up to 50 people," and handed out certificates to staff members of the communications team, ITV reported.

For the past week, Johnson has been buffeted by multiple claims that social events were held inside 10 Downing Street in the runup to Christmas 2020, when the United Kingdom was under stringent coronavirus regulations that outlawed such activities.

CNN contacted Downing Street and Doyle independently for comment on the latest reports. However, both replied saying "there is an ongoing review, and we won't be commenting further while that is the case."

The controversy deepened markedly on Tuesday with the emergence of a video broadcast by ITV News from the time that appears to show Number 10 officials joking about a party during a rehearsal for televised press briefings.

In the December 2020 video, Allegra Stratton, who was at the time Johnson's spokeswoman, refers to a Christmas party, at a time when the UK was under strict lockdown conditions that limited gatherings and effectively canceled Christmas.

On Wednesday Stratton resigned from her government position in a tearful statement.

Stratton, who later served as the Prime Minister's COP26 spokeswoman, said her comments had become a "distraction" in the fight against coronavirus, and offered her resignation on Wednesday afternoon. "I understand the anger and frustration that people feel," she said in a statement on camera.

"To all who lost loved ones, endured intolerable loneliness and struggled with your businesses -- I am sorry and this afternoon I offered my resignation to the Prime Minister."

Also, on Wednesday, Johnson announced to Parliament that his cabinet secretary would conduct an investigation, which will now look into at least three separate alleged gatherings.

The Prime Minister apologized "unreservedly for the offense" the leaked video had caused, but said he had been "repeatedly assured that there was no party and no rules were broken." Johnson said that if rules were broken "there will be disciplinary action for all those involved." He added that he was "furious" when he saw the video.

Downing Street's position, before and since the video was leaked, is this: "There was no Christmas party and coronavirus rules had been followed at all times."

After speaking to multiple officials, CNN has established that social gatherings were indeed held on the two days in question -- November 27 and December 18 -- and has confirmed a Daily Mirror report that Johnson himself gave an impromptu speech at the first one. Sources also confirmed reports that secret Santa gifts were exchanged on December 18.

The accusations are damaging for the government as it seeks to enforce tougher coronavirus restrictions. On Wednesday, Johnson announced England would be tightening restrictions -- to a set of rules called "Plan B" -- due to rising cases of the Omicron coronavirus variant.

From Friday, face coverings will again become mandatory in most public venues, including movie theaters. And from next week people will be advised to work from home and present a "Covid Pass" proving vaccination or recent recovery to enter nightclubs and other venues with large crowds.

- by Sharon Braithwaite and Allegra Goodwin, CNN