Westminster is salivating in expectation of electrifying theatre. “It will be mandatory viewing,” says one former cabinet minister. “We will all be watching.” Just after lunchtime this Wednesday, Alexander Boris de Pfeffel Johnson will be in the dock for contempt of parliament, a charge which could result in his expulsion from it. He will have to answer to multiple counts of lying to the Commons about Partygate when he faces televised interrogation by the seven MPs of the privileges committee. There will be a lot at stake at what is expected to be a marathon inquisition. The bereaved families of Covid casualties and everyone else outraged by this scandal have had a long wait for the moment when Mr Johnson is finally held to official account for the deceptions he deployed to try to cover up Partygate. A guilty verdict from the committee will resonate around the world because it is highly likely to lead to his eviction from the Commons. That would be a first for this country. No ex-prime minister has ever been expunged from parliament in that way. It would also surely mean the extinction of his ambitions to return to Number 10. As importantly, if not more so, this is a fundamental test of whether parliament is capable of protecting its integrity and our democracy from abuses of power by deceivers like him. He has often maintained he is blithely relaxed about the day of reckoning that he will face this week, but this is an interrogation the accused has been dreading. We know this because he has hired expensive lawyers, at a chunky cost to the taxpayer, to advise him on how to save his skin. We also know this because of the desperate efforts made by him and his gang to try to suppress and discredit investigation of his misconduct. The first gambit, which happened when he was still clinging on at Number 10, was to try to block a referral to the privileges committee, an attempt that failed when a large number of Conservative MPs refused to be complicit in what would have been a cover-up of a cover-up. Having failed to prevent an investigation, there was then what looked like an endeavour to stymie it. When the committee sought evidence from Number 10, it was either not provided or produced in a form so heavily redacted as to be useless. Only towards the end of last year did the committee finally get the material it needed to do its job properly. As the committee has gone about its work, taking witness statements, examining exchanges between Number 10 personnel and gathering other material, the Johnson gang has rubbished it as a “witch-hunt” and a “kangaroo court”. These attacks on the committee, which has a mandate from and proceeds with the authority of the Commons as a whole, are arguably a contempt of parliament in themselves. From my soundings, the committee’s members have been angered, and understandably so, by this campaign to undermine them. Their job description is clear. They are not deciding whether or not there were illegal gatherings in Number 10 during the pandemic. Everyone everywhere knows that law-breaking was rampant in Downing Street. We’ve seen the incriminating photographs, read the damning witness statements and are aware that the police issued 126 fines, including one on Mr Johnson himself, for what the Met commissioner at the time called “serious and flagrant” breaches of the rules. The committee doesn’t have to decide whether or not the former prime minister misled parliament. Everyone everywhere knows he did and on several occasions. On 1 December 2021, he told the Commons that “all guidance was followed completely in No. 10”. We know this and other statements, such as “the rules were followed at all times”, were simply untrue. The committee’s job is to judge whether his denials were the result of an innocent misapprehension about the lockdown-busting that went on in Number 10 or whether he told deliberate lies to MPs. The verdict the committee is leaning towards seems clear from its interim report published a fortnight ago. This concluded that it would have been “obvious” to Mr Johnson that the law was being flouted inside Number 10, especially when he himself was present at rule-busting parties. Witness testimony has him telling one packed gathering inside the building, which took place at a time when lockdown restrictions were very strict, that it was “probably the most socially undistanced gathering in the UK right now”. Upon publication of that interim report, he claimed it “totally vindicates me”, which was extreme truth-inversion even by his standards. The report was condemnatory and it is important to note that the four Conservative members of the committee put their signatures to it along with the three MPs from opposition parties. “That’s a bad harbinger for Boris,” reckons one senior Tory. The privileges committee isn’t often in the spotlight and has never before been so centre stage. The Labour chair of this inquiry, Harriet Harman, is a highly experienced politician and its senior Tory, Sir Bernard Jenkin, has been an MP for more than 30 years. Yet neither of them, let alone the lesser-known members of the body, have ever been involved in anything of this magnitude. We must hope that they have done their homework and have their wits about them for what will be a significant test. For their individual reputations, and that of the Commons which they are representing, they need to handle this interrogation effectively. “The committee will really have to be on the top of its game,” says one privy counsellor. Encouragingly, they have spent a lot of time assessing the evidence and have also put in some hours rehearsing how they intend to conduct their inquisition of the former prime minister. That’s sensible given the slippery character of the accused. It was one of Mr Johnson’s friends who once dubbed him “the greased piglet” in tribute to his capacity to slither his way out of the tightest of spots. On past form, he will claim that he attended alcohol-fuelled gatherings in the belief they were legal “work events” and relied on “assurances” from others that everything was within the rules. He has never been specific about who gave him those “assurances”. Was it Dilyn the dog? There’s a mountain of evidence suggesting that both he and senior staff at Number 10 must have known that the law had been broken before he denied it to parliament. To take just one of many examples, there’s an exchange between officials in which his director of communications says: “I’m struggling to come up with a way this one is in the rules.” The majority of the public and most MPs concluded long ago that he lied about Partygate. It is nevertheless important that the committee deploys the evidence in a forensic way which leaves him with no place to hide and his remaining apologists no space to carry on protesting his innocence. “He’s quite difficult to interrogate, Johnson, because it’s all bluff and bluster,” says a senior parliamentarian with experience of doing so in a committee format. “They will need to pin him down.” If the committee recommends his suspension from parliament for 10 or more sitting days, and the Commons ratifies that sanction, then he’s looking at the drop. A recall byelection will be triggered so long as a petition for one is signed by at least a tenth of his constituents in Uxbridge and South Ruislip. He would then have to decide whether to quit or contest the seat. Forecasts currently suggest that he’d lose it by a hefty margin. So Wednesday is going to be a big day. We may be witnesses to the beginning of the end of Boris Johnson’s parliamentary career and his lie-strewn odyssey through British political life. That’s huge. Even more crucially, the Commons has an opportunity that it must seize to protect itself and us from mendacious government. It is a basic premise of our democracy that the executive is held to account by parliament. That foundation is destroyed if ministers think they can get away with deliberately misleading MPs. When those in power believe that they can deceive with impunity, it becomes impossible for parliament to do its job on behalf of the people. That is hideously corrosive for democracy and public faith in it. This is why it is so essential that the penalties for lying to parliament must be steep and especially severe when the perpetrator has lied, and on a grave issue, from the highest office in the land. It is not just the fate of a disgraced prime minister that is at stake. It is the credibility of parliament, the trustworthiness of our political culture and the health of our democracy. Andrew Rawnsley is Chief Political Commentator of the Observer