Published: 2022-05-25 17:06:30 BdST
The report by senior official Sue Gray was commissioned by Johnson after revelations of alcohol-fuelled parties at Downing Street when social mixing was all but banned under stringent laws his government had made to curb the spread of COVID-19.
"Many of these events should not have been allowed to happen," the report said. "The senior leadership at the centre, both political and official, must bear responsibility for this culture."
Gray's interim findings were published in January, but most details were withheld until the end of a separate police inquiry, which concluded last week with 126 fines handed out.
Both Johnson and finance minister Rishi Sunak were among those fined over a party to celebrate the prime minister's 56th birthday on June 2020.
Johnson has faced calls from opposition politicians and some in his own party for him to resign after it was revealed both he and officials had broken the rules which meant people could not socialise outside their households or even, in many cases, attend funerals for loved ones.