Boris Johnson’s loyal band of supporters continue to believe he is the only politician with the box-office appeal to turn around the Tory party’s ailing fortunes. Before he has any chance of plotting a comeback, however, he will have to endure another box-office encounter that represents his biggest obstacle. In what will be a high-stakes spectacle, major broadcasters are planning to air the entirety of the former prime minister’s testimony to parliament’s privileges committee, which is examining whether he misled MPs about law-breaking parties during the Covid pandemic. So much sensitive evidence has been submitted to the inquiry that the Observer has been told it is being kept in a “strong room”. Only those with proper passes and reasons for access are allowed in and out. One source said some of the claims about parties were “decidedly weird”, and that new information would come to light. Meanwhile, Johnson’s eagerly anticipated appearance – which could be one of only a small number of public hearings – will happen later than originally planned as a result of the quantity of documents the committee has been given. He is now expected to appear before the cameras next month. This will be broadcast live on parliament’s televised feed, and Sky News is already understood to have decided to show his whole evidence session. The stakes have been raised in recent weeks as Johnson has broken cover with a series of speeches and appearances, some designed to keep his supporters onside and others to cash in since leaving office – a process he has described to friends as putting “hay in the loft” before he can embark on a comeback. Last week, he recorded a £1m donation to his office from Christopher Harborne, a Thai-based British businessman who had previously given millions of pounds to Nigel Farage’s Brexit party. He and his family are also being supported by the billionaire Bamford family, who have provided Johnson with two homes declared as costing £10,000 each for the month. The events that took place in Whitehall during the pandemic are already being raised ahead of the privileges committee examination. Last week, Johnson was accused of joking at one leaving party during lockdown that “this is the most unsocially distanced party in the UK right now”. He repeatedly told MPs that he did not know gatherings broke Covid laws in place at the time. A spokesperson for Johnson did not deny the comment but said the then prime minister had “worked constantly” to ensure the government did all it could to save lives and protect livelihoods during the pandemic. Whatever happens during the live questioning of Johnson during the inquiry, some MPs believe there is also a serious problem ahead for Rishi Sunak over the parties inquiry. MPs will have to vote on any sanction on Johnson recommended by the cross-party committee. While it is likely to be a “free” unwhipped vote, some MPs said that, in reality, Tories would seek advice over how they should vote. One Labour MP predicted the event would end up being a “win-win” for Keir Starmer. “Let’s say that the committee decides the House was misled and Johnson is either forced to apologise to the House or suspended,” they said. “The government has to table a motion on that. Will they be whipping people to support it, or to vote down a Labour amendment designed to increase the sanction against him? They will be terrified about what to do. If he doesn’t defend Johnson, Johnson could try to take Sunak down. If he does defend him, the voters will take a dim view.” Should Johnson navigate the privileges inquiry and retain support within the Tory party, some MPs are speculating that he may attempt to switch seats as his current Uxbridge and South Ruislip constituency is a winnable target for Labour. One of his options is to secure a seat from one of the supporters he has placed in the House of Lords. They include Nadine Dorries and Nigel Adams, both of whom have safe Tory seats. Their elevation to the Lords is understood to have been delayed until closer to the election, to avoid hard byelections for the government.