Government lawyers have sought to rely on the European convention on human rights – maligned by many Conservatives – to avoid having to hand over unredacted files to the Covid inquiry. At an unprecedented high court challenge to the demand by the inquiry chair, Lady Heather Hallett, for documents that include the entire WhatsApp history of Boris Johnson and a former No 10 aide, Henry Cook, James Eadie KC argued it would “breach article 8 rights”. In written arguments, the government’s advocate said: “Article 8 … prohibits unnecessary or disproportionate intrusion into an individual’s private and family life. The protection of personal data is of fundamental importance to the right under article 8 … In the context of judicial proceedings, the European court of human rights has found violations of article 8 where a domestic court has included sensitive personal information within its judgment which was not ‘rendered strictly necessary by the specific features of the proceedings and by the facts of the case’.” Conservatives including the home secretary, Suella Braverman, and the former deputy prime minister Dominic Raab have long mooted leaving the convention. On Thursday there were renewed calls to do so after the decision in the Rwanda deportations case. The court of appeal ruled on Thursday that the plan to send asylum seekers to Rwanda to have their claims processed was unlawful because it breached article 3 of the convention, which prohibits torture and inhuman or degrading treatment. In response, the former cabinet minister Simon Clarke suggested the UK should “revisit the question of our membership”. Sir Edward Leigh, the veteran backbencher, demanded a “derogation” from the convention. Replying, Braverman said Leigh “makes a very powerful point” and criticised the European court of human rights, which interprets the convention and halted the first attempt at sending a flight to Rwanda, for having operated in a way that was “opaque, irregular and unfair when it comes to the will of the British people”. Article 8 has been a particular bugbear, with the likes of Raab claiming it is unfairly relied on by foreign criminals to avoid deportation. In written arguments, Eadie, who is asking Lord Justice Dingemans and Mr Justice Garnham to quash Hallett’s demand, also argued that forcing the government to hand over all of the files requested would breach GDPR provisions, which concern data protection. He described the chair’s assertion that all documents covered by the notice were “potentially relevant” as “an untenable, irrational conclusion”. Eadie said: “The Cabinet Office has never disputed that WhatsApp messages containing, or relating to, key pandemic decision-making are relevant and disclosable. Those are precisely the type of messages disclosed and not redacted. “It is messages which do not concern pandemic decisions which are irrelevant, and yet caught by the over-broad notice. Compelling the provision of every WhatsApp over a two-year period, without any subject matter qualification, is absurd.” Hugo Keith KC, representing Hallett, said in written submissions that the Cabinet Office’s interpretation of her powers was “flawed and unworkable” and “undermines the chair’s ability to fulfil her statutory terms of reference, both fully to investigate the facts and also to make effective recommendations for the future.” He said: “It effectively leaves the holder of the documents, and not the chair, patrolling the boundary of what is relevant to the chair’s investigation. It would have serious implications not only for the ongoing work of this inquiry but for the conduct and operation of all current and future statutory inquiries.” Johnson, an interested party in the case, reiterated his willingness to comply with Hallett. The former prime minister’s lawyer, Lord Pannick KC, said in his written arguments: “Mr Johnson has no objection to the inquiry inspecting the materials unredacted, subject to appropriate security and confidentiality arrangements having been put in place, given the personal and sensitive nature of some of the material.” The judges will give their ruling at a later date but said they would attempt to reach a decision “as quickly as possible”.