Boris Johnson’s former aide Dominic Cummings is set to appear before the Covid inquiry on Tuesday.
Mr Cummings, who served as Mr Johnson’s chief adviser, and former communications chief Lee Cain are among the senior political figures who will give evidence at the inquiry this week.
Martin Reynolds, Mr Johnson's principal private secretary who sent an invite to a "bring your own booze" gathering in the No 10 garden, will also give evidence.
Mr Cummings is already on the record being fiercely critical of Mr Johnson's approach, not least his reluctance to sign off a second nationwide lockdown in late 2020.
It comes amid reports that sexist messages allegedly sent by Mr Cummings and Mr Johnson are set to become public at the inquiry this week.
Ex-Tory Chancellor George Osborne said the exchanges could further tarnish the Government’s reputation.
Speaking on the Political Currency podcast, Mr Osborne said: “From what I understand, there are some pretty staggering things that have been said on those WhatsApp messages not just by Boris Johnson, but key advisers like Dominic Cummings.
"Really pretty disgusting language and misogynistic language. And I think if you didn't think very highly of that period of government, you're going to think even less highly after you've heard those messages next week.
A spokesman for Mr Johnson reportedly denied the former Prime Minister sent any misogynistic messages.
Reports also claim that messages could be published from the UK’s top civil servant, Cabinet Secretary Simon Case, in which he accuses Mr Johnson of being “mad” in July 2022 when the then-PM was pushing to end social distancing.
A WhatsApp exchange at the time revealed Mr Case said Mr Johnson wanted to declare "we're over Covid". Mr Case reportedly said the claim would be "Trump-Bolsonaro level mad and dangerous", referring to ex-presidents of the US and Brazil, Donald Trump and Jair Bolsonaro.
Mr Cummings was Mr Johnson’s closest aide when the pandemic began. The Government was forced to defend him after he drove to County Durham beauty spot Barnard Castle during the first lockdown.
But he left Downing Street in November 2020 after a dispute with Mr Johnson and has since become a critic of the former prime minister, suggesting he was indecisive in the response to Covid.
Mr Cummings used his latest Substack post to reveal he had been going through his statement with inquiry lawyers, describing the process as “painful”.
“I finally sent it in on Thursday. I give evidence on 31/10,” he wrote earlier this month.
