Some Conservative MPs have urged Boris Johnson to resign over his admission he attended a drinks event during the Covid lockdown, but others have said they are waiting to hear Sue Gray's verdict.
The senior civil servant is carrying out an investigation into alleged Covid rule breaking in Downing Street and government departments.
According to the inquiry's terms of reference, the purpose of Ms Gray's probe is to establish "a general understanding of the nature" of gatherings that took place and whether any "individual disciplinary action" should be taken.
Her report, which ministers say will be published shortly, is likely to be a largely factual account of any gatherings, and she cannot rule on whether lockdown laws were broken.
The findings will be made public, but not necessarily the full report.
If the inquiry uncovers evidence of behaviour that is potentially a criminal offence, it will be referred to the Metropolitan Police and the inquiry will be paused.
And if there is evidence a minister has breached the code of conduct, it could be investigated by the prime minister's standards adviser Lord Geidt (although he would need Mr Johnson's permission before launching a new inquiry).
Catherine Haddon, of the Institute for Government think tank, warns the report won't settle the issue.
She says Ms Gray may "touch on the role of the prime minister but it isn't [her] place to judge his behaviour".
And while many in government have praised Ms Gray's professionalism, she has still been given the difficult job of investigating her bosses - not only the prime minister, but also potentially Simon Case - the head of the civil service - who stepped down from leading the investigation after reports a party was held in his own office.
The civil servant does at least have plenty of experience in government including investigating - and in some cases condemning - powerful ministers.
'A lady called Sue'
In his memoir, the former Liberal Democrat minister David Laws recalls being told by fellow minister Oliver Letwin: "It took me precisely two years before I realised who it is that runs Britain.
"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."
Ms Gray joined the civil service straight from school and worked her way up to the Cabinet Office, where for six years, she led the government's Propriety and Ethics team which provides advice to government departments on standards issues.
Polly Mackenzie - who worked as a special adviser in the Cabinet Office - told the BBC's Profile programme in 2017 : "Sue has been there for so long, she knows everything that anybody has ever done wrong."
Gus O'Donnell, a former head of the civil service, said: "If there is any one person in the civil service who could write their memoirs, hers would be the most valuable, the most priceless and the most sensational.
"I am extremely confident that such a memoir will never be written - her secrets will go to the grave."
Downing Street party row
- ANALYSIS: What was really going on in No 10 during lockdown?
- LAURA KUENSSBERG: What next for Johnson after party apology?
- REALITY CHECK: What rules did Downing Street party break?
- PROFILE: Party investigator Sue Gray
- TIMELINE: Alleged government lockdown gatherings
In 2017, one of her investigations forced Damian Green - at the time one of Theresa May's most senior ministers - to step down after he was found to have made "inaccurate" statements over what he knew about claims pornography was found on his office computer in 2008.
She also investigated claims of sexual misconduct by the minister towards journalist Kate Maltby, ruling that her claims had been "plausible".
Speaking to the BBC, Ms Maltby said: "What impressed me most about Sue Gray was how seriously she took her duty of care to complainants... she was determined to listen to junior people, and not let senior staff off the hook.
"I found her profoundly moral in a way that isn't normally seen in Westminster. But she is someone who has spent her life operating in Whitehall, and her report will be limited by the norms of civil service language, the parameters of the task given to her, and by some compromises, especially on transparency, only if minor compromises are required for her to push through her key ethical findings".
Ms Gray's knowledge of ministers' private interests is said to have been useful to prime ministers carrying out rejigs of their ministerial team.
Chris Cook - an ex BBC journalist who now works for news website Tortoise - said one sign of a forthcoming reshuffle would be when Sue Gray's office furniture had been re-arranged.
After 20 years, she left the Cabinet Office on secondment to work at the finance department in Northern Ireland's government.
When a job to lead the Northern Ireland civil service became available she applied, but didn't get it.
Unusually for a normally private individual, she gave an interview to the BBC admitting she was "disappointed" she didn't get the top job and suggested she may have been seen as "too much of a challenger, or a disrupter".
Last year she returned to the Cabinet Office leading on matters related to the Union and the Constitution.
She may have spent the bulk of her career in the civil service, but in the late 1980s she did take a career break to run a Northern Ireland pub called the Cove Bar, along with her husband the country and western singer Bill Conlon.
She told the BBC: "I loved it, loved it at the time, I'd never do it again."
But the experience may prove useful in her current role. As a family friend told the Mail's Michael Crick "if a pub landlady doesn't know what a party is, who will?"