The prime minister's former top aide Dominic Cummings has said Boris Johnson was warned about No 10 holding a drinks party during lockdown.
Mr Cummings - who has been strongly critical of Mr Johnson since he left No 10 - says the PM "waved aside" concerns about the gathering.
Mr Johnson has admitted he attended the event on 20 May 2020, but says he believed it was work-related.
No 10 said it was "untrue" to say Mr Johnson was "warned about the event".
A Downing Street spokesman added: "As he said earlier this week, he believed implicitly that this was a work event. He has apologised to the House and is committed to making a further statement once the investigation concludes."
Last week, Mr Johnson said he went to the gathering in the Downing Street garden and stayed at the drinks for 25 minutes to thank staff for their hard work.
No 10 said it was "untrue" to say Mr Johnson was "warned about the event".
A Downing Street spokesman added: "As he said earlier this week, he believed implicitly that this was a work event. He has apologised to the House and is committed to making a further statement once the investigation concludes."
Last week, Mr Johnson said he went to the gathering in the Downing Street garden and stayed at the drinks for 25 minutes to thank staff for their hard work.