A cabinet minister has piled pressure on the government to hand over Boris Johnson’s unredacted WhatsApp messages to the Covid inquiry, saying it should be allowed to “get on with its job”. Grant Shapps, the energy secretary, said there was “nothing to be shy or embarrassed about” for ministers who were trying their best to grapple with the first pandemic in a century. As the 4pm deadline for the Cabinet Office to hand over the files loomed, he called for the inquiry to be given “whatever they want”. “There are things which we did that were very good,” Shapps told TalkTV. “Things will have gone wrong, naturally. The inquiry is there to get to the bottom of all of that.” Johnson handed over a trove of documents – including notebooks and WhatsApp messages – on Wednesday. His team say the Cabinet Office did have access to the details for months and had been invited to view them on multiple occasions at his office. But the move poses a serious headache for the prime minister, Rishi Sunak, given the government may be forced to take legal action if it wants to avoid handing over the information. The case is viewed as a litmus test, and senior government figures fear if they acquiesce then more requests could be made for workbooks and WhatsApps from ministers who are still serving. A potential judicial review was discussed at top-level meetings on Wednesday, the Guardian has been told. But Tory MPs have urged the government to climb down and hand over the files, or else seek a compromise with Heather Hallett, the chair of the Covid inquiry. Tobias Ellwood, the chair of the defence select committee, also on Thursday called for the government to hand over the WhatsApp messages. He said Lady Hallett was a “formidable KC”, but added that ministers should consider their use of the messaging platform “because there are no rules governing that, but there are with official minutes” of meetings. Hallett was also backed by Lord Saville, who chaired the public inquiry into Bloody Sunday, which lasted 12 years. He said the decision about what evidence was relevant to the Covid inquiry was “for her and nobody else”. “If she simply accepts the word of somebody else that the material is irrelevant, she will not, in my view at least, have done as thorough a job as she should have,” Saville told Times Radio. “You couldn’t get anybody more trustworthy and able to judge the relevance or irrelevance of the matter than Heather Hallett. She is an absolutely first-class judge, in whom I have complete faith.” The Cabinet Office maintains it has already decided what information is relevant, and has handed over 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.”