Johnson admitted for the first time he had attended the party at Downing Street on May 20, 2020, when social gatherings were limited to a bare minimum and said he understood the anger that the revelations had caused.
"I know the rage they feel with me over the government I lead when they think that in Downing Street itself the rules are not being properly followed by the people who make the rules," Johnson told parliament on Wednesday (January 12).
Johnson, who won a landslide 2019 election victory on a promise to secure Britain's exit from the European Union, said he regretted his action and had thought the gathering was a work event.
"I went into that garden just after six on the 20th of May 2020 to thank groups of staff before going back into my office 25 minutes later to continue working," he said. "With hindsight, I should have sent everyone back inside."