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Following claims that he also hosted his own parties during lockdown, Simon Case, the civil servant leading an inquiry into the No. 10 Christmas party breached lockdown has now stepped down.

No. 10 said Simon Case had removed himself from the process "to ensure the ongoing investigation retains public confidence". He will be replaced by veteran civil servant Sue Gray, second permanent secretary at the communities and levelling up department.

The disclosure comes as a significant embarrassment to Downing street, which has been engulfed by a series of scandals in recent weeks, as well as the embarrassment of losing the North Shropshire byelection to the Liberal Democrats.

A report by Mr. Simon into the alleged party was due for publishing as soon as this week. However, plans plunged into doubt after it emerged that a Christmas event for staff had taken place in his (Mr. Simon case) office just a day before the alleged Downing street party.

Some outlets allege that staff from both the Cabinet Office and other departments were mingling in Case�s office and an outside room on 17 December last year, a day before the No. 10 party he has been investigating. The occasion is said to have included drinks, snacks and Christmas decorations.

A Cabinet Office statement said staff in Case�s private office took part in �a virtual quiz� on that date. It said: �A small number of them, who had been working in the office throughout the pandemic and on duty that day, took part from their desks, while the rest of the team participated virtually.

�The Cabinet Secretary played no part in the event but walked through the team�s office on the way to his own office. No outside guests or other staff were invited or present.

Mr Case, who has been cabinet secretary since last September, had been asked by Prime Minister Boris Johnson to investigate gatherings for staff in government buildings last year.

Is Mr. Boris to blame?

His inquiry was focusing on events in Downing Street on 27 November, 15 December and 18 December, and at the education department on 10 December. His role will be replaced by Sue Gray.

Labour's deputy leader Angela Rayner said she was incredibly disappointed Mr Case "didn't come clean" when he was first tasked to investigate alleged parties in Downing Street - and that his replacement Ms Gray had an "incredible responsibility to restore trust".

Ms Rayner said the issue of departmental parties now appeared to be endemic but that it was the prime minister who "set the tone" for the government and had "allowed it to happen under his watch".

The prime minister allegedly spent about 15 minutes with staff at the alleged social gathering on 15 May 2020, telling one aide inside No 10 that they deserved a drink for �beating back� coronavirus.

Sources claimed about 20 staff drank wine and spirits and ate pizza following a press conference on that day, some in offices inside No 10 and others going into the garden. It is also alleged that some staff stayed drinking until late into the evening.