Sue Gray is the woman charged with looking into the most explosive allegations in politics in recent years.
She has been tasked with investigating whether there were repeated breaches of lockdown rules at Downing Street and other Whitehall departments when the UK was in lockdown.
Since allegations first came to light, the Prime Minister has admitted he was at an event on May 20, 2020. He told the Commons he stayed for 25 minutes and maintains he did not know an event was planned but said he should have ended it when he saw it was happening. Mr Johnson said he "believed implicitly" that it was a "work event".
However his former aide Dominic Cummings has said the Prime Minister lied to the Commons and that he knew the event was breaking rules. You can read the latest on that here.
When is the report going to be published?
There is no confirmed date yet, but some discussion its publication is imminent.
In Prime Minister's Questions on Wednesday, January 19, the Prime Minister told Commons colleagues the report would be "next week" suggesting it will come out in the week of January 24.
The official document published in December which lays out what she can look at and what action can be taken said it needs to be completed "swiftly".
What has she done before?
She first joined the Cabinet Office in the late 1990s.
She served as the Director General, Propriety and Ethics in the Cabinet Office from 2012 to 2018.
Before joining the Cabinet Office, Ms Gray worked in Transport, Health and DWP covering a range of roles which included both policy and front line delivery. Sue also took a career break in the late 1980s when she bought and ran a pub in Newry, Northern Ireland.
In May 2021 she returned to the Cabinet Office to take up the role of Second Permanent Secretary with responsibility for the Union and Constitution Directorate. Prior to that from 2018 to 2021 she served as the Permanent Secretary of the Department of Finance, NI Executive on secondment from the Cabinet Office.
What does the review look at?
When it was announced, the inquiry was due to look at alleged gatherings inside Downing Street on November 27 and December 18 2020, as well as one at the Department for Education on December 10. There is also the party the Prime Minister attended on May 20. Mr Johnson and Downing Street have refused to answer a number of key questions about that event saying that it would be covered by Ms Gray's inquiry.
The full terms of reference for the inquiry adds: "Where there are credible allegations relating to other gatherings, these may be investigated".
"The primary purpose will be to establish swiftly a general understanding of the nature of the gatherings, including attendance, the setting and the purpose, with reference to adherence to the guidance in place at the time. If required, the investigations will establish whether individual disciplinary action is warranted.
Who can she talk to?
The Cabinet Office say: "The team will have access to all relevant records, and be able to speak to members of staff."
It adds: "All Ministers, Special Advisers, and civil servants will be expected to co-operate with the investigations. Any staff with information relevant to the investigations should provide it to the Cabinet Office investigation team."
What if people are found to have broken rules?
"As with all internal investigations, if during the course of the work any evidence emerges of behaviour that is potentially a criminal offence, the matter will be referred to the police and the Cabinet Office’s work may be paused. Matters relating to adherence to the law are properly for the police to investigate and the Cabinet Office will liaise with them as appropriate. Any matters relating to the conduct of Ministers should follow the process set out in the Ministerial Code in the normal way.
"Pastoral care and support will be provided to all staff involved. The findings of the investigations will be made public. Following the long-standing practice of successive administrations, any specific HR action against individuals will remain confidential," the document continues.
There has been criticism that as Ms Gray ultimately answers to the Prime Minister and it cannot therefore be an independent inquiry.
Can the Prime Minister be sacked?
Ministers found to have lied in the Commons usually resign, but this is only a matter of convention. Deputy Prime Minister Dominic Raab is one of those who has said that a minister should resign if they have lied to Parliament.
However, if it is proved, for example, that the Prime Minister has lied, his party and backbenchers also wield power. Tory MPs can submit letters of no confidence in Mr Johnson to the chair of the backbench 1922 committee, Sir Graham Brady. Conservative Party rules state that if 15% of Tory MPs (54) submit a no-confidence letter a leadership contest can be triggered.
Then there would be a vote of no confidence which the PM would need 181 MPs to back him in to survive.
The number of letters with Sir Graham is confidential, however, we know five MPs have called for him to quit. We've asked Welsh Conservative MPs where they stand.
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