Boris Johnson’s deputy has insisted the prime minister did not breach the ministerial code even though he was penalised by police for attending a No 10 party in lockdown, as the government’s ethics chief reportedly threatened to quit over the scandal. Dominic Raab, the deputy prime minister and justice secretary, said on Wednesday that Johnson had only “unintentionally” and “inadvertently” broken the law by attending a birthday gathering in No 10 during lockdown, which led to him being given a fixed-penalty notice. He said this did not amount to a breach of the ministerial code, despite the prime minister’s ethics chief, Lord Geidt, querying whether it had been. Geidt’s future in the role is in doubt after he said it was a “legitimate” question whether Johnson had breached the code. In response, the prime minister made clear in a letter to Geidt that he did not believe the code had been broken. The prime minister is still the only one who can give permission for an ethics inquiry, and he made clear on Tuesday his intention to block one into his own conduct over the fixed-penalty notice. The row with Geidt is the latest headache for the prime minister as he faces a wave of discontent from his MPs over the fixed-penalty notice. More than 40 Tory MPs have publicly questioned Johnson’s fitness to hold office, including 18 who are known to have sent letters to Sir Graham Brady, the chair of the 1922 Committee of Conservative backbenchers, to formally seek a confidence vote. The remainder have openly called for the prime minister to resign or said they had lost faith in his leadership. However, the Cabinet Office insisted Geidt was not resigning. A No 10 source added that the release of Johnson’s letter on Tuesday had drawn a line under the issue, after a meeting between the pair. The source said there was “frustration” in Downing Street at the “failure of communications” that meant the prime minister had not understood earlier that Geidt was expecting him to release a statement. “It hadn’t been raised with him that he needed to make a public comment,” they said, adding: “The PM’s letter speaks for itself.” Raab said he did not believe there would be a vote of no confidence against Boris Johnson next week. He told Sky News: “I just don’t see that. I think the Westminster bubble and village whips this stuff up. I’m not saying it’s not serious and significant. But we dealt with all of those issues, the prime minister has dealt with all those issues.” Speaking to broadcasters, Raab said Geidt had “made clear a number of concerns but the prime minister has addressed them in his response and in particular made clear the explanation that he didn’t believe he’d broken the ministerial code”. “In relation to the single fixed-penalty notice, it had been an unintentional breach of the law and inadvertent in the sense that he turned up to the gathering without having realised it would be in breach of the relevant regulations. Raab did not deny that Geidt had threatened to quit, saying he was “not privy” to conversations about it. It comes after Johnson rebuffed calls for Geidt to have the power to launch his own investigations into the conduct of the prime minister or other members of the cabinet. Last week, Johnson also changed the code to make clear that ministers should not necessarily have to resign even if they are found to have breached the code, suggesting apologies or loss of pay as alternative remedies. Raab also pointed out that Lady Scotland was allowed by Gordon Brown to keep her job as attorney general in 2009, despite having been fined for employing a housekeeper who had stayed in the country illegally. “I’m just saying there are precedents for this … I think it’s clear from the circumstances of this particular gathering, where he turned up, was there for 10 minutes, was unaware that it was a surprise birthday cake for him, that wasn’t a deliberate breach of the rules, and that’s the key point,” Raab told Times Radio.