The former prime minister has been the focus of much of the evidence given to the inquiry recently, with many of his one-time colleagues taking aim at his leadership during the Covid pandemic.
So, after weeks of damning evidence, here’s what Johnson will probably be asked.
Did Boris Johnson understand the gravity of Covid at the start of 2020?
Johnson played down the initial impact of the virus in early 2020, publicly saying he had shaken hands with multiple people who had Covid.
He also failed to attend early Cobra meetings on the government’s response to the approaching pandemic.
His one-time aide, Dominic Cummings, previously told a parliamentary committee that Johnson of not understanding how serious the illness was and so “tens of thousands of people died who didn’t need to die” because the then-PM locked down too late.
The inquiry has already heard how, in a diary entry written on September 19, 2020, then chief scientific adviser Patrick Vallance wrote: ”[Johnson] is all over the place and so completely inconsistent. You can see why it was so difficult to get agreement to lock down first time.
Johnson’s former director of communications Lee Cain sent a message to Cummings in early 2020 claiming the PM “doesn’t think [Covid] is a big deal and he doesn’t think anything can be done and his focus is elsewhere”.
The message added: “He thinks it’ll be like swine flu and he thinks his main danger is talking economy into a slump.”
Who really made the key decisions in No.10?
Top senior civil servant Simon Case speculated that Johnson’s wife, Carrie Johnson, was the “secret PM”, while former chancellor Sajid Javid told the inquiry that Dominic Cummings was “prime minister in all but name”.
Case also told a WhatsApp group of senior officials in September 2020 that the government looked like a “tragic joke” run by a “weak team”, with Johnson changing “strategic direction every day”.
He added: “Government isn’t actually that hard, but this guy is really making it impossible.”
Meanwhile Cain said the pandemic was the “wrong crisis” for Johnson’s skill set.
Was Johnson sceptical about Hancock?
Then health secretary Matt Hancock was at the core of Johnson’s decision-making team until he was forced to resign for breaking the social distancing rules himself in 2021.
Hancock has been heavily criticised throughout the inquiry, with the former chief executive of NHS England, Sir Simon Stevens, saying Hancock “took the position that in this situation he, rather than the medical profession or the public, should ultimately decide who should live and who should die”.
Former senior civil servant Helen MacNamara also said Hancock “regularly” told colleagues things “they later discovered weren’t true” – a claim also echoed by Cummings when he gave evidence.
What does Johnson say to the claims he was ‘bamboozled’ by Covid science?
In his pandemic diaries, Vallance wrote that Johnson had “looked broken” and held his “head in his hands a lot” at the height of Covid.
“The prime minister at the time gave up science when he was 15,” Vallance also told the inquiry. “I think he would be the first to admit it wasn’t his forte.”
He later added: “It was hard work to make sure he had understood what a particular graph or piece of data was saying.”
Meanwhile, Cummings claimed in his written evidence to the inquiry that the PM was distracted by his divorce at the start of 2020, his “financial problems” and his then-girlfriend wanting to “finalise the announcement of their engagement”.
What was the culture of Downing Street really like?
In WhatsApp messages presented to the inquiry as evidence, Case criticised the “madness” of the government at the time and said the team was “basically feral”.
MacNamara, who has since left her job, also told the inquiry Johnson oversaw a “toxic culture” in No.10, where “obvious, sexist treatment” of women was common.
The former deputy cabinet secretary said the “dominant culture was macho and heroic” and “contaminated by ego”.
Johnson’s failure to stop this behaviour, she added, was “miles away from what is right, or proper, or decent, or what the country deserves”.
What impact does he think Partygate had?
Johnson, his wife and current PM – then the chancellor – Rishi Sunak were all fined for attending a rule-breaking party at the height of Covid.
MacNamara told the inquiry that Covid rules were broken every single day in Downing Street.
“I would find it hard to pick one day when the regulations were followed properly inside that building,” she said.
She said only during the weekly cabinet meeting were the rules – made by the government – actually followed.
“And everybody moaned about it and tried to change it repeatedly,” she added. “So I know how exceptional it was to really, really, really properly follow the guidance.”
Did he really...
1. Say ‘let the bodies pile high’?
Giving evidence to the Inquiry, Lord Eddie Lister, former chief of staff and long-term ally to Boris Johnson, said he heard Johnson say this during a meeting in September 2020.
Johnson has previously denied making such a statement.
2. Ask if a hairdryer up the nose would kill Covid?
Johnson’s former aide, Dominic Cummings claimed Johnson once asked about a rather DIY method to eradicate Covid.
“A low point was when he circulated a video of a guy blowing a special hair dryer up his nose ‘to kill Covid’ and asked the CSA (chief science adviser) and CM (chief medical officer) what they thought,” Cummings said.
3. Call the Treasury ‘the pro-death squad’?
In January 2021, Johnson used this term to describe the Treasury when describing the tiers system in a meeting, according to Vallance’s diaries.
“And he ends it by saying the team must bring in the pro-death squad from Her Majesty’s Treasury,” counsel to the inquiry Dermot Keating read out.
4. Think old people should ‘accept their fate’ and catch Covid?
Writing in his diary on August 28 2020, Vallance said: ”[Johnson] is obsessed with old people accepting their fate and letting the young get on with life and the economy going. Quite a bonkers set of exchanges.”
The inquiry also revealed that a former aide to Johnson believed the ex-PM had asked “why are we destroying the economy for people who will die anyway soon” in the early days of the pandemic.
5. Write ‘bollocks’ over health guidance documents?
In October 2020, Boris Johnson wrote “bollocks” in capital letters across a Department of Health guidance document about the impacts of long Covid.
He has since admitted that he did not the illness “truly existed” at the time.
What will Johnson say?
Reports from sources close to Johnson suggest he intends on apologising to the inquiry – but maintain that he got the big calls right, particularly the vaccine programme and how the UK came out of the final lockdown quite quickly.
He is also expected to defend his turn of phrase because it helped him get the best out of his team.
His written statement is approximately 200 pages long, and – according to the BBC – barely mentions Cummings.