Labour deputy leader Angela Rayner was present when Sir Keir Starmer was caught on video drinking a beer with party workers during lockdown, the party has said.
The party acknowledged it had previously told journalists she was not at the event last year, but a source insisted it was a “mistake made in good faith”.
A Labour spokesman said no Covid rules had been broken at the gathering, which took place in the Durham constituency office of the local MP.
Tory MPs have been pressing police to reconsider their decision not investigate the event following the fine issued to Boris Johnson for attending a birthday gathering in No 10.
Durham Police confirmed they have received “a number of further communications” which they will be responding to, but said they are not currently investigating the matter.
The gathering – which included an online Labour Party event – took place on April 30 last year in the constituency office of the City of Durham MP Mary Foy.
The Daily Mail reported that when its reporters approached party officials in January, they had been told Ms Rayner was not present.
However after it produced video evidence that she had joined Sir Keir at the gathering, they admitted she had been there.
A Labour source told the PA news agency it had been a “genuine mistake”, while a spokesman said there was “no comparison” with the parties which took place in No 10 and Whitehall.
He said: “Keir Starmer was in the workplace, meeting a local MP in her constituency office and participating in an online Labour Party event.
“They paused for food as the meeting was during the evening. No rules were broken.
“There is simply no comparison between standing in a kitchen having something to eat between meetings, with multiple, flagrant rule breaking drinks parties at the heart of Government, dismissed by lies at the despatch box and resulting in an apology to the Queen.”
