The COVID public inquiry is set to become explosive this week, with former Boris Johnson aide Dominic Cummings expected to dish the dirt on the former prime minister.

The maverick former No 10 adviser, once Mr Johnson‘s closest ally but now his sworn enemy, heads a list of top former Downing Street insiders giving evidence this week.

The ghost-like figure of Mr Cummings is due to give evidence on Halloween, prompting claims that he will face haunting questions on everything from “partygate” to lockdowns.

The No 10 insiders being quizzed include former private secretary Martin Reynolds, nicknamed “party Marty” after writing a notorious “bring your own booze” email to Downing Street staff.

Mr Reynolds is the first witness this week, followed in the afternoon by former director of communications Lee Cain, a former tabloid journalist who now calls himself an expert in crisis management.

Mr Cummings takes centre stage on Tuesday, in a session of evidence expected to be as sensational as his marathon public appearance before a committee of MPs two years ago.

Then he claimed Mr Johnson initially did not take COVID seriously and changed his mind 10 times a day and that former health secretary Matt Hancock should have been sacked for lying.

He also admitted that his own controversial trip to Barnard Castle, in County Durham, when he had COVID in 2020 – and his much-ridiculed claim that it was to test his eyesight – had been a “terrible mistake”.

‘This week really matters’

This week Mr Cummings is expected to launch further brutal attacks on Mr Johnson, as well as the former PM’s wife Carrie, Mr Hancock and cabinet secretary Simon Case.

Mr Case will be a notable absentee during the current round of evidence sessions, on how decisions were made in government, as he is currently away from work on sick leave.

This week’s hearings are also expected to see the publication of embarrassing WhatsApp messages sent between key Downing Street figures including Mr Cummings and Mr Johnson.

A number of damaging WhatsApps have already been released to the inquiry, including how Mr Johnson described long COVID as “b*******” and that his wife, Carrie, had been described as “the real person in charge” by Mr Case.

Last week it was also revealed that scientific advisers had referred to Rishi Sunak – who was then the chancellor – as “Dr Death” following the Eat Out to Help Out scheme.

In addition, the former Conservative chancellor, George Osborne, has claimed “disgusting and misogynistic” WhatsApp messages sent by Mr Johnson and Mr Cummings will be released this week.

Sunak and Johnson expected to attend inquiry

Previewing this week’s evidence on the Politics at Jack & Sam’s podcast, Sky News deputy political editor Sam Coates said: “What is going to happen this week really matters, not least because there are people who are at the heart of this inquiry who are still in government.

“I understand that Rishi Sunak is likely to appear before the COVID inquiry in December, possibly 11th December. Boris Johnson will appear around then too.

“But the big figure who is going to come out, possibly the worst of everybody from the evidence that we hear over the next few days, is someone who is currently off sick. That’s the cabinet secretary, Simon Case.

“We’re going to see more WhatsApp messages between him and those two key political advisers, Lee Cain and Dominic Cummings, which basically tell a story of how, at the height of the pandemic when there was chaos through 2020, you had these two key figures along with the cabinet secretary complaining about and to some degree working against the prime minister who employs all three of them.”

Click to subscribe to Politics At Jack And Sam’s wherever you get your podcasts

Coates added: “What you’ll hear this week from figures like Dominic Cummings and Lee Cain, but particularly Dominic Cummings, is a lot of score-settling. A lot of attacks on Boris Johnson, attacks on Matt Hancock, attacks on bits of the civil service, the Cabinet Office, that weren’t working.

“But if you step back, what you really see is a completely dysfunctional No 10, with the prime minister on one side and his closest advisers seemingly working against him.”

Read more from Sky News:
Matt Hancock talks about ‘injustice’ he faced during COVID
Humza Yousaf says in-laws are alive in Gaza but without water

Other witnesses giving evidence this week include:

• Imran Shafi, former private secretary to the prime minister;
• Helen MacNamara, former deputy cabinet secretary;
• Lord Stevens of Birmingham, who as Sir Simon Stevens was boss of NHS England;
• Sir Christopher Wormald, permanent secretary of the Department of Health and Social Care;
• Professor Yvonne Doyle, former director for health protection at Public Health England.

Cummings has shunned use of lawyer

This week’s hearings are likely to cast the spotlight on a time which was critical for the country but expose what went on behind the door of Downing Street, with revelations that are sure to be capitalised upon by Labour.

After the examples of “laddish, football-style” banter between Mr Case and Mr Cain, it is understood there are likely to be further such examples this week, which could be highly damaging to Mr Case’s position.

Sky News also understands that in preparing for his testimony, Mr Cummings, the former chief adviser to the prime minister, has shunned the use of a lawyer, which could leave him exposed to challenges to his testimony from other witnesses.