One reveller stayed in No 10 until 4.20 am at a notorious party in which a swing in the Downing Street garden was broken, the Sue Gray report has found.
Another left just after 3am, her long-awaited findings show.
The report found that individuals were encouraged to leave by the rear exit of No 10, but some “remained in the building and carried on drinking alcohol until the early hours”.
“Exit logs indicate that some left after midnight and others between 01.45-02.45. Two members of staff stayed later still, with one leaving at 03.11 and the last leaving at 04:20” the report states.
The prime minister has been accused of presiding over Covid lockdown breaches on a “record-breaking scale”, after the Metropolitan Police issued 126 fines for events over eight dates during its investigation into the partygate scandal.
Mr Johnson himself received just a single fine, over his birthday party during lockdown.
Sue Gray also said that she had learned of multiple examples of “unacceptable” treatment of security and cleaning staff during her investigation into partygate.
“I found that some staff had witnessed or been subjected to behaviours at work which they had felt concerned about but at times felt unable to raise properly,” she wrote.
“I was made aware of multiple examples of a lack of respect and poor treatment of security and cleaning staff. This was unacceptable.”
Labour frontbencher Emily Thornberry has called for today to “be the day” Mr Johnson resigns.
Speaking to Times Radio, she said he could not “front” this out by “wriggling and lying and trying to drag other people in” to cover up for his own actions. “Today should be the day he takes responsibility for coming to Parliament and lying to us.,” she said.
“Our democracy depends on politicians not being allowed to lie like that.
Ms Thornberry added: “He should do the right thing today and resign.”