LONDON — The UK's top civil servant has stepped aside from his role leading an inquiry into Downing Street lockdown parties, after it emerged an event was held in his own office.

Simon Case had been due to report on claims COVID-19 rules were broken at events for staff last year. But his role was put into doubt after reports a party was held in his office while London was under COVID rules.

No. 10 said the probe would be concluded by senior civil servant Sue Gray. Gray is the second permanent secretary at the Department for Levelling Up, Housing and Communities.

A spokesperson for No. 10 said: "To ensure the ongoing investigation retains public confidence the Cabinet secretary [Simon Case] has recused himself for the remainder of the process".

They said Gray would "ascertain the facts and present her findings to the prime minister".

The BBC understands a quiz was held for members of Case's private office on Dec. 17, 2020, and invites were sent out titled "Christmas Party!"

About 15 people were invited to the gathering at 70 Whitehall, near Downing Street, although it is understood not everyone turned up.

Responding to the claims, a government spokesperson said: "Staff in the Cabinet secretary's private office took part in a virtual quiz on Dec. 17, 2020.

"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 were virtual.

"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. This lasted for an hour and drinks and snacks were bought by those attending. He also spoke briefly to staff in the office before leaving."

The party was first reported on the Guido Fawkes website on Friday afternoon.

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.

His inquiry was focusing on events in Downing Street on Nov. 27, Dec. 15 and Dec. 18, and at the education department on Dec. 10.

This investigation was supposed to clear up whether rules had been broken — and many hoped it would allow the government to move on.

Instead, it rumbles on and on. We are seeing more allegations — right up to the office of the man who was given the job of investigating.

It is deeply embarrassing for the government — and for the Cabinet secretary — that he is now seen to have a conflict of interest in this inquiry.

The big picture is that Boris Johnson has faced a torrid few weeks, which have left his party jittery.

The list is long; the handling of sleaze allegations, the record Tory rebellion in the Commons, the loss of an incredibly safe seat, the continued fallout from allegations of Christmas parties in Whitehall.

Christmas cheer will be in short supply in the Conservative Party this year. And many MPs will be hoping the prime minister makes some significant New Year's resolutions to steady the ship.

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

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 Scottish National Party's Westminster leader, Ian Blackford, told BBC Two's Newsnight that "having somebody else from the civil service marking their own isn't good enough" and that it should be someone with authority from outside the government and civil service.

"I would suggest that the best way to do that would be by having a judge-led inquiry," he added.

Labour MP Chris Bryant, who is chairman of the Commons standards committee, told BBC Radio 4's Today program he was not convinced about Gray leading the investigation and a "completely independent figure" should be chosen instead.

However, Lord Barwell, a former Conservative MP who was chief of staff for then-Prime Minister Theresa May, said he could not think of a better person for the role, adding that she was "completely independent" and he was confident "we will get the facts". — BBC