Boris Johnson is accused of personally attending a cocktail party at Park 10 during the first lockdown.
Downing Street did not immediately deny a report in the Sunday Times alleging that the Prime Minister attended the potentially rule-breaking event with his wife, Carey, in May 2020.
The newspaper quoted three sources that Johnson’s chief private secretary, Martin Reynolds, emailed officials with the hostess invitation “BYOB,” which means bring your own bottle, or drink wine.
Chief Civilian Sue Gray is investigating the May 20 event as part of her investigation into several allegations related to rule-breaking events held at No. 10 during the coronavirus pandemic.
Allegations of that gathering, which was said to have been attended by 40 people, surfaced this week when Dominic Cummings said he warned at the time that “socially isolated drinks” would likely be against the rules and “should not happen”.
But a front-page report that Mr Johnson himself was present would add to the allegations.
The Prime Minister imposed England’s first Covid-19 lockdown in March 2020 and groups of up to six people were not allowed to meet outdoors until 1 June.
Labor deputy leader Angela Rayner said: “It appears that a culture of total disregard for the rules has taken hold in Downing Street since the start of the pandemic.
“When so much of the country was struggling with empty shelves and total lockdown with no meeting with others, it seems like we’ve been No. 10 hosting parties from the start.
“Boris Johnson and his team are taking the country as idiots. We need Sue Gray’s independent investigation report as soon as possible, and Boris Johnson must face the consequences of his actions.”
Ms Gray, a senior Cabinet Office official, also expanded its investigation to a park gathering on May 15, 2020 which was revealed by a leaked photo showing the Prime Minister and staff sitting around cheese and wine.