But appearing in public for the first time after days of Covid self-isolation, Johnson also ducked questions about whether he would resign if an internal inquiry establishes that he did lie.
Johnson is battling damaging allegations that he and staff attended boozy events during Covid restrictions, prompting an investigation by senior civil servant Sue Gray.
The revelations have sparked public fury, leading to a double-digit lead in polls for the main opposition Labour party over Johnson's Conservatives, and calls from some Tories for him to quit.
Johnson has apologised for a party on May 20, 2020 in the Downing Street garden, telling parliament last week he thought it was a "work event", despite an aide inviting staff to "bring your own booze".
But his combative former senior adviser Dominic Cummings, who has been waging a vendetta against Johnson since leaving Downing Street in late 2020, said he warned his then boss about the event at the time.
"I can tell you categorically that nobody told me, nobody said this was something that was against the rules, that it was a breach of the Covid rules, that it was something that wasn't a work event," Johnson said.
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