Ministers have been accused of writing a “blank cheque” for Boris Johnson’s legal bills, as it emerged taxpayer-funded support was being extended to help defend him against claims he misled parliament over Partygate. With just days left until a contract expires with the law firm Peters and Peters, which Johnson and the government have relied on to disparage an investigation by the privileges committee, the Guardian has learned the Cabinet Office intends to renew it. The extension could be for up to six months given the investigation’s slow progress and was likely to be signed off without a new tender process, sources said. Peters and Peters was given the four-month contract, worth nearly £130,000, in August. David Pannick, an advocate and king’s counsel, was instructed on the firm’s behalf. The life peer has since sought to discredit the investigation by claiming MPs on the cross-party committee had adopted a “fundamentally flawed approach” and that their interpretation of whether any misleading was deliberate would have a “chilling effect” on future statements by ministers. Johnson himself has protested his innocence, and is said to believe it is unclear what the committee is investigating. The Peters and Peters contract expires on 16 December, but sources confirmed it would be extended to help Johnson and the government while the privileges committee inquiry continued. They said procurement rules meant that because the same service was being requested, the government would not need to re-tender the contract. The Cabinet Office declined to say whether more money would be spent on the extended contract, or if the legal advice would continue to be provided within the existing budget. Angela Rayner, Labour’s deputy leader, said Rishi Sunak had “serious questions to answer” about whether more taxpayer cash would be spent defending Johnson during a cost of living crisis. “Families up and down the country who are struggling to make ends meet will rightly be outraged at this sickening waste of their money,” she told the Guardian. Rayner said despite Sunak’s pledge to restore integrity and accountability to government, he was “already failing to stop the rot in Downing Street” and pointed out that the government had still not appointed an ethics adviser. Oral evidence sessions, which were meant to begin by the end of November, were now not likely to begin until mid-January. Johnson himself would be called to give evidence, and was said to have requested he be accompanied at the hearing by a legal team – something a source close to him denied. Because the privileges committee is in control of the timetable for witness sessions, requests for follow-up evidence and the writing of its final report, the contract extension could be for up to six months. While delays to the inquiry were caused by the death of the queen and wrangling over the addition of a new member to the committee, the government was also accused of delaying things by refusing to hand over, or heavily redacting, key documents. Chris Bryant, a Labour MP and chair of the standards committee, suggested Johnson could afford to pay his own legal bills and highlighted the money the former prime minister has made since leaving office, including a speech for which he charged £276,130. “The government seems to have issued a blank cheque to Boris Johnson at a time when public finances are meant to be tight,” Bryant said. “Frankly, Boris Johnson can afford his own legal representation.” Ministers have previously said public money is being used to defend Johnson, even though he is no longer a member of the government, because the inquiry “has potential implications for all future statements by ministers of the crown in current and future administrations”.