Boris Johnson has handed over a major cache of WhatsApp messages and notebooks to the Cabinet Office, challenging it to release the documents unredacted to the Covid inquiry. In a move that will pose a major headache for the government, Johnson suggested Whitehall officials should “urgently disclose” the contents to the public inquiry. His provocation came as senior Conservatives urged the government to back down and avoid a protracted legal battle over the issue. William Wragg, who chairs the Commons constitutional affairs committee, said the inquiry had “the powers and authority to request evidence it sees fit to consider”, and that the Cabinet Office should “comply with both the spirit and the letter of how the inquiry is constituted”. Robert Buckland, a former justice secretary, instead called for a compromise “to avoid an ugly turf war”. “There needs to be disclosure with agreed redactions,” he said. “I support the government argument about the need for ministers and officials to work in a safe space but the inquiry has agreed terms of reference and is entitled to ask for material relevant to the ambit of its work.” As the pressure mounted, Cabinet Office officials were scrambling to respond to the Covid inquiry chair, Heather Hallett, by her 4pm deadline on Thursday. She has demanded WhatsApp messages and notebooks from Johnson and texts from one of his No 10 aides, Henry Cook. The government has been resisting, in part because some senior figures fear more potential requests could follow concerning other ministers who are still in post. It emerged earlier this week that the government had previously been in possession of Johnson’s documents, but after officials looked through the files and decided they were not relevant to the inquiry, the Cabinet Office said it no longer had them. Johnson said in a statement on Wednesday afternoon that the Cabinet Office had had access to the material for months. It is said that government officials and their lawyers were invited to his offices to view the files on a number of occasions. Further material was provided to the Cabinet Office this week, and Johnson’s spokesperson said he was “perfectly happy for the inquiry to have access to this material in whatever form it requires”. They also said he had cooperated with the inquiry in full and looked forward to continuing to do so. Rishi Sunak was urged to confirm that the full documents would now be given to the inquiry. Labour’s deputy leader, Angela Rayner, said the Cabinet Office had run out of excuses and should stop trying to conceal the truth. “If other ministers are hoping to hide behind the same smoke and mirrors tactics to dodge public scrutiny by the inquiry, it is increasingly clear they don’t have a leg to stand on,” she said. The Liberal Democrat MP Christine Jardine said: “He can’t use Boris Johnson any more as an excuse to avoid handing over vital evidence. Bereaved families are still waiting for answers. They deserve so much better than yet another Conservative stitch-up.” Given officials fear the issue is a litmus test and that handing over Johnson’s files could mean other ministers would have to do the same, they may be forced to challenge Lady Hallett’s ruling in the courts. A judicial review was said to be becoming more likely, but taking legal action against the head of a public inquiry at such scale would be unprecedented. Jonathan Jones, a former head of the government legal department, said officials should not refuse to share the documents to save ministers’ blushes. Hallett has requested messages Johnson exchanged with about 40 people, including Sunak. “I’m sure that it won’t be at all surprising if some of this ministers would prefer not to disclose, because it’s politically embarrassing or personally embarrassing,” Jones said. “That wouldn’t be very surprising because you’re talking about potentially a large amount of material, some of it on personal devices. But those are not reasons for withholding it. If it’s relevant, it should be disclosed.” Robin Butler, a former cabinet secretary and head of the inquiry into intelligence about Iraq’s weapons of mass destruction, said he thought Hallett was being “pretty unreasonable”. He said: “When I did my inquiry on WMD and we had to winkle information out of the government, I followed the precedent of the Falklands inquiry and asked the permanent secretary of each department to give their personal undertaking that all information that was relevant would be released to us. That worked and subsequently I never discovered anything that wasn’t released that should have been.” Stephen Reicher, a behavioural scientist who advised the government during the Covid pandemic, said the standoff was symptomatic of ministers’ lack of understanding of the importance of trust. “If there is anything that is more corrosive of trust than releasing information which shows rule breaking, it is to be seen to try and hide information about rule breaking,” he said. “It takes us for fools at two levels, the information that is being hidden and what is being hidden. What is more, once we have lost trust and we think of government as the ‘other’, as venal and corrupt, the blacked-out passages lead us to imagine unlimited transgressions which are probably worse than what did go on.” The Cabinet Office maintained it had already provided more than 55,000 documents, 24 personal witness statements and eight corporate statements to Hallett’s inquiry. It has argued: “We are firmly of the view that the inquiry does not have the power to request unambiguously irrelevant information that is beyond the scope of this investigation. This includes the WhatsApp messages of government employees’ which are not about work but instead are entirely personal and relate to their private lives.”