The long awaited report has piled pressure on the Prime Minister and said the public would be “dismayed” by the breaches across Downing Street and Whitehall.
It also revealed Mr Johnson joined five special advisers in a meeting with “food and alcohol” in his Downing Street flat on the evening of the announcement of Dominic Cummings’ departure.
The Metropolitan Police has issued 126 fines for rule breaches in No 10 and Whitehall, with the Prime Minister receiving a single fixed-penalty notice for his birthday party.
She said some of the more junior officials who attended parties “believed that their involvement in some of these events was permitted given the attendance of senior leaders”.
Ms Gray continued: “The senior leadership at the centre, both political and official, must bear responsibility for this culture.
She also said there were “multiple examples of a lack of respect and poor treatment of security and cleaning staff” during the events, which was “unacceptable”.
The senior civil servant added: “Many will be dismayed that behavior of this kind took place on this scale at the heart of Government.
“The public have a right to expect the very highest standards of behavior in such places and clearly what happened fell well short of this.
“The events that I investigated were attended by leaders in government. Many of these events should not have been allowed to happen.
It also revealed a No 10 special adviser warned the Prime Minister’s principal private secretary, Martin Reynolds, that it would be “helpful” if people avoided “walking around with bottles of wine” ahead of the Bring Your Own Booze party on May 20 2020 as it was taking place after a press conference.
The report states: “[A] No 10 special adviser sent a message to Martin Reynolds by WhatsApp at 14.08 stating ‘Drinks this eve is a lovely idea so I’ve shared with the E & V team who are in the office. Just to flag that the press conference will probably be finishing around that time, so helpful if people can be mindful of that as speakers and cameras are leaving, not walking around waving bottles of wine etc.’
“Martin Reynolds replied ‘Will do my best!’”
On Mr Cummings, she conceded she only collected “limited” information because she had only begun gathering details on it when the Metropolitan Police launched an inquiry and did not return to it.
She wrote: “Following the announcement of the departure of Dominic Cummings and Lee Cain, a meeting was held in the No 10 flat from some time after 18.00 to discuss the handling of their departure. Five special advisers attended.
“The Prime Minister joined them at about 20.00. Food and alcohol were available. The discussion carried on later into the evening with attendees leaving at various points.”
She said she concluded “it was not appropriate or proportionate” to make further inquiries after the Met investigation.
Mr Johnson will apologize to MPs in a Commons statement later.
George Holan is chief editor at Plainsmen Post and has articles published in many notable publications in the last decade.