Labour deputy leader Angela Rayner did attend an event where Sir Keir Starmer was caught on camera drinking beer with activists during lockdown, the party has confirmed.
Labour acknowledged it had previously told journalists Ms Rayner was not present at the gathering last April when coronavirus restrictions were in force.
But a party source said it was a “mistake made in good faith”.
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A Labour spokesman said no COVID rules had been broken at the meeting, which took place in the Durham constituency office of the local MP Mary Foy in the run-up to the Hartlepool by-election.
At the time, people in England were banned from mixing indoors apart from for work.
Richard Holden, the Conservative MP for North West Durham, has 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.
But Labour has rejected that there is any equivalence with the Downing Street partygate scandal, which has rocked the government.
Durham Police confirmed it had received “a number of further communications” that it will be responding to, but said it is not currently investigating the matter.
Speaking to Sky News, Labour’s shadow chief secretary to the treasury Pat McFadden said: “The police have already looked at this in Durham and, they’ve found nothing to take action on.
“And, you know, people are trying to draw some equivalence to this, but the police have already looked at it. And that’s been their conclusion.
“I simply don’t believe that this is equivalent in any way to a series of parties – bring your own booze, booze being brought in by the suitcase with ABBA singing Winner Takes It All in the background.
“The attempt to draw equivalence is to try to absolve this – they want people to think it’s all the same so no scandal matters. And that’s a bad place to go.”
Meanwhile, Mr Holden has said he has accepted an apology from Ms Foy after she had “drunkenly” abused him on the Commons terrace on Tuesday night for asking police to review claims Sir Keir broke lockdown rules.
The incident, reportedly witnessed by several people, happened as MPs waited for late-night votes.
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In a statement posted on Twitter, Mr Holden said: “Mary Kelly Foy has given me a wholehearted apology after, unprovoked, she drunkenly approached, berated and grabbed me on the terrace of parliament on Tuesday evening in front of other MPs and members of staff.
“I have accepted her apology and consider the matter closed.”
A party source confirmed Ms Foy had issued a personal apology.