Boris Johnson will face tough questioning from the Privileges Committee on Wednesday regarding claims that he misled parliament in relation to the partygate row.
As the former prime minister prepares to give evidence, all eyes are on the coming session.
Mr Johnson is expected to mount a strong defence in response to the accusations.
The hearing can be watched live on Parliamentlive.tv, but it is expected that most news channels will screen the proceedings due to their high-profile nature.
To prepare for this high-stakes hearing, here are the key facts you need to know.
The role of the Privileges Committee
The role of the Privileges Committee in the House of Commons is to consider matters relating to parliamentary privilege, which is a set of legal protections and immunities that MPs and peers enjoy so that they can carry out their parliamentary duties effectively.
The committee has been asked to conduct an investigation to determine whether Mr Johnson provided false information to MPs regarding the partygate scandal.
They will be responsible for making recommendations to the House of Commons on how to deal with such breaches.
The committee has members from all parties represented in the House of Commons and is chaired by a senior MP who is usually a member of the governing party. It operates independently of the government and is guided by long-standing principles of parliamentary privilege and procedure.
Who leads the committee?
The committee is chaired by Harriet Harman. A prominent figure in British politics since 1982, Ms Harman holds the distinction of being the longest-serving female MP and a former cabinet minister.
Known for her advocacy of gender equality and women's rights, Ms Harman has been an advocate of gender parity in politics throughout her career. She has held various roles in government and senior positions in the main opposition Labour Party, including that of deputy leader.
With her impending departure from politics at the next general election, Harman's tenure as chairwoman of the Privileges Committee will be closely watched by political observers. Her leadership is expected to bring a strong focus on upholding parliamentary standards and accountability.
Ms Harman has represented Camberwell and Peckham for many years and previously served in the cabinets of Tony Blair and Gordon Brown.
She was appointed to lead the investigation into Mr Johnson's conduct after Chris Bryant recused himself due to public remarks criticising the former prime minister.
Other members of the committee
The committee comprises a group of experienced MPs from various parties.
One of the members is Bernard Jenkin, a Conservative who has served in parliament since 1992 and is known for his criticisms of the former prime minister's handling of certain issues.
Despite being a vocal supporter of Brexit and an ally of Mr Johnson, Mr Jenkin has staunchly upheld the impartiality of the committee's investigation into partygate. In the past, he led the European Research Group of Eurosceptics.
He has defended the committee against attacks from Mr Johnson's allies, characterising their attempts to discredit the investigation as a “terrorist campaign”. Mr Jenkin has emphasised that it is their responsibility to pursue the inquiry.
Another Conservative member is Alberto Costa, who has represented South Leicestershire since 2015. He was previously a junior government minister under Theresa May but was fired in 2019 over an amendment he proposed to Brexit legislation.
He later resigned from a junior role under Suella Braverman when she was attorney general to avoid a conflict of interest with his investigation of Mr Johnson.
Last year, he spoke out against the “breakdown in good governance” during Mr Johnson's premiership and urged Tory leadership candidates to show how they would improve standards.
The committee also includes Labour's Yvonne Fovargue, who has held several shadow ministerial roles and joined the body in September 2021. Last year, Ms Fovargue, who had previously resigned from her position on the Labour front bench due to her opposition to Brexit, was appointed as a cross-party trade envoy to Tunisia and Libya.
Allan Dorans, the sole Scottish National Party member on the committee, has represented Ayr, Carrick and Cumnock since 2019. Mr Dorans is a former detective inspector for the Metropolitan Police and has experience in investigating allegations of wrongdoing.
He is known for his calls for justice for the murdered police officer Yvonne Fletcher. Although he has not commented publicly on partygate, he has criticised Mr Johnson's former aide Dominic Cummings in the past for his lockdown visit to Barnard Castle, stating that people must have confidence that the government is following its own rules.
Standing down at the next election, Charles Walker is another independent-minded Conservative backbencher who gained attention for his emotional criticism of the Truss administration's chaotic final days. He is a respected backbencher on the Tory benches, and he announced last year that he intends to retire from politics at the next election due to the “toxic environment” in politics.
Conservative MP Andy Carter, who was elected in 2019 to represent Warrington South, is another member of the committee. He was elected in 2019 as part of the “Red Wall” Tory wave, and had a junior government role as parliamentary private secretary at the Department for Work and Pensions.
However, he resigned last year to prevent a conflict of interest in his role investigating Mr Johnson. He stated that if Johnson was found in contempt, he would be required to resign and that the inquiry could only conclude with a resolution from the House of Commons.
He also stressed the importance of maintaining the integrity of the parliamentary process by not discussing matters under consideration.
Anticipated questions for Boris Johnson's hearing
The committee has made it clear that the inquiry's focus is to determine if Johnson misled Parliament, rather than delving into the various details of the partygate scandal.
As a result, questions are expected to centre on the written evidence contained in the committee's interim report and Mr Johnson's defence.
This includes WhatsApp messages given to the inquiry which reveal advisers struggling with the party rules, with one admitting that an excuse “blows another great gaping hole in the PM's account.”
The committee has stated that “the evidence strongly suggests that breaches of guidance would have been obvious to Mr Johnson at the time he was at the gatherings.”
A “core bundle” of documents, which both the panel of MPs and Mr Johnson may refer to during questioning, will be released later on Wednesday.
Anticipated defence of Boris Johnson
Mr Johnson has consistently denied any wrongdoing and has rejected the notion that he intentionally or recklessly misled Parliament.
He presented his main defence in a 52-page document, emphasising that he trusted the assurances of his key advisers and that “hindsight is 20/20.”
In his defence, he mentions the “cramped” working conditions at No 10 Downing Street and his belief that no guidelines or regulations were being violated at any gathering.
Mr Johnson places a great deal of confidence in the assurances he received as prime minister and says that no one around him raised any concerns.
He says there is no evidence that he was ever warned about guideline breaches.
Additionally, he questions the scope and impartiality of the committee's investigation.
How is the government responding to the hearing?
Although Prime Minister Rishi Sunak has announced that he will not be watching the proceedings and will not attempt to sway MPs on the committee, he is expected to allow a free vote in the Commons on any recommended sanctions.
However, if Mr Johnson is found in contempt and sanctions are recommended, this could pose a challenge for the current prime minister.
Despite the continuing investigation, Mr Johnson still enjoys support within the Conservative Party and from members of Mr Sunak's Cabinet.
The recent staunch defence of Mr Johnson by Northern Ireland secretary Chris Heaton-Harris and Home Secretary Suella Braverman's praise of the former prime minister have raised eyebrows.