Staff carried on drinking in Number 10 until the early hours at parties on the eve of the Duke of Edinburgh’s funeral, with the last person not leaving until 4.20am, the Sue Gray report said.

The two leaving dos which began the evening before the Queen sat alone in St George’s Chapel at Windsor Castle as her husband of more than 70 years was laid to rest were among the notorious episodes in the partygate affair.

At around 6.30pm on April 16, about 45 people – including a few attending online – gathered in the press office to mark the departure of communications chief James Slack. Wine and beer had been brought in by staff.

Around the same time, a smaller event for another departing staff member started in the basement, with wine laid on and music playing from a laptop computer placed on top of a printer.

In the course of the evening the two groups mingled, eventually joining together in the Downing Street garden, with more than 20 people still present with a number of bottles of alcohol at 9.30pm.

At that point the group began to break up, with some people leaving after being encouraged by the No 10 custodians to depart by the rear exit.

However others returned to the building where they carried on drinking until the early hours.

Exit logs indicated some left after midnight and others between 1.45am and 2.45am, with two staying on later – with one leaving at 3.11am and the last departing at 4.20am.

When staff returned in the morning it was noticed and reported that a child’s swing/slide in the garden had been damaged by people leaning on it.