(Bloomberg) -- Boris Johnson’s former top aide Dominic Cummings accused the premier of lying to Parliament, saying he would “swear under oath” that the premier both was aware of and allowed a drinks party at Downing Street at the height of lockdown during the first wave of the Covid-19 pandemic.

It’s the latest tirade by Cummings against his former boss since he was forced from his position 14 months ago. His Jan. 7 post about a Downing Street party on May 20, 2020 attended by Johnson forced the prime minister to apologize in the House of Commons and left him fighting to save his career.

Now Cummings is again upping the ante, by saying Johnson misled lawmakers.

In his statement last week, Johnson said he thought he was attending a “work” gathering and that he only stayed for 25 minutes. His office has also repeatedly said the prime minister was not aware of the event beforehand, and did not receive the widely reported “bring your own booze” email invitation from his principal private secretary, Martin Reynolds. 

After several newspapers reported over the weekend Johnson had been urged not to let party go ahead, his spokesman Max Blain reiterated it was “not accurate” to suggest he knew about the May 20 event. “It’s untrue to say that the prime minister was told or warned ahead of that,” he said.

Yet hours later, Cummings wrote on his blog that Johnson not only knew about the party but agreed with Reynolds it should go ahead after “at least two” people raised concerns. “Not only me but other eyewitnesses who discussed this at the time would swear under oath this is what happened.”

“The events of 20 May alone, never mind the string of other events, mean the PM lied to Parliament about parties,” Cummings said.

The charge is especially sensitive because many Tory MPs have said they are waiting for the result of a government probe into the party -- as well as other allegations of pandemic rule-breaking in Downing Street -- before deciding whether Johnson has misled them and whether they still back his leadership.

Rules banning social gatherings were still in place in May 2020 as the U.K., which suffered one of the world’s biggest death tolls from coronavirus, battled to contain the first wave of the pandemic. 

Johnson’s administration has been dogged by reports of other parties that broke regulations. In December, the prime minister told the House of Commons he had been “furious” to see a clip of Downing Street aides joking about a Christmas party during the second lockdown -- but said he had been “repeatedly assured” there was “no party and no Covid rules were broken.”

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