Sue Gray is a senior civil servant and Second Parliament Secretary in the Cabinet Office.

From 2012 until 2018 she served as the UK Government’s director general of its propriety and ethics team where she was described as "the most powerful person you've never heard of".

During her time on the propriety and ethics team in 2017, former Prime Minister Theresa May charged her to investigate Conservative MP Damian Green over allegations that he had lied about pornographic images on his Commons computer.

She also led the so-called "plebgate" inquiry into claims that Andrew Mitchell, who was at the time the chief whip, had insulted police officers in Downing Street.

She was also the permanent secretary of the Department of Finance in Northern Ireland from 2018 to 2021, before returning to the Cabinet Office to her current role and is now the most senior civil servant at the new Department for Levelling Up.

Last year she suggested that she missed out on Northern Ireland’s top civil service job as she is “too much of a challenger”.

Government officials have described her as the “best person” to lead the current enquiry.

Liberal Democrat minister David Laws, who was part of the 2010 coalition government, said Oliver Letwin once told him that Ms Gray was the brains behind the UK government operation.

In his memoirs, Mr Laws quotes Mr Letwin as saying: "Our great United Kingdom is actually entirely run by a lady called Sue Gray, the head of ethics or something in the Cabinet Office.

"Unless she agrees, things just don't happen. Cabinet reshuffles, departmental reorganisations, the whole lot - it's all down to Sue Gray.

"Nothing moves in Whitehall unless Sue says so."

After civil servant Simon Case stepped down from leading the ‘partygate’ enquiry in December 2021 after it emerged he had attended one held in his own office, Sue Gray took over and is now to determine who attended the party on May 20, 2020, as well as any other party-related issues.

Currently, it is not known who attended the Downing Street party, but Ms Gray is tasked to find out the information.

Her role is extremely important as the findings of her investigation could have huge implications on Boris Johnson’s political future and how it is reported by the media.

While Ms Gray’s job is to establish the facts, once she has reported - which could be as early as next week - it will be up to the Prime Minister, other ministers and MPs to determine what happens next.

Speaking today about the inquiry, Jacob Rees-Mogg described Ms Gray as "a civil servant of the highest integrity and of the greatest reputation".

If Ms Gray does decide that coronavirus rules were broken, the police could potentially become more heavily involved and Scotland Yard is already in touch with the Cabinet Office over the alleged party.