Some of the WhatsApps and diaries that the Cabinet Office went to court to avoid revealing to the Covid inquiry were in fact “relevant” to proceedings and can be made public, the chair has ruled, after examining them for herself.

Heather Hallet’s judgement, which is legally binding, comes after the government released all of the unredacted notebooks and WhatsApps to her confidentially so that she could make a decision on their contents.

The Cabinet Office had claimed some passages were “unambiguously irrelevant” and should be exempt from the order to hand over evidence.

But in a legal decision published today, Hallett said certain passages from Johnson’s diaries, notebooks and WhatsApp messages, and others from his aide’s WhatsApp messages, were useful to the inquiry despite claims that they were not within the scope of its investigations.

Hallett did, however, agree that most of the material was irrelevant to the inquiry and therefore would not be used as evidence, marking a partial win for the government department after it lost its bid to hang onto the unredacted evidence in July.

Having seen the unredacted evidence herself, Hallett said: “The great majority of the passages initially identified by the Cabinet Office as ‘unambiguously irrelevant’ are… irrelevant. That said, the overlap is not total. There are some passages that I consider are relevant, in the sense that they relate to matters in question at the inquiry, that the Cabinet Office had marked as ‘unambiguously irrelevant’.”

The inquiry considered 29 sets of WhatsApp exchanges between Johnson and other individuals, and a group chat, as well as 34 separate threads and 67 exchanges in group chats from Henry Cook, Johnson’s adviser at the time. Some exchanges are as long as 100 pages.

Evidence considered also included Johnson’s diaries, with detailed, typed appointments for every day between 1 January 2020 and 31 January 2022, and his notebooks containing contemporaneous manuscript notes made by him over a similar period, constituting 35 files.

Not included in this legal tussle are Boris Johnson’s WhatsApp messages from the first stages of the pandemic. These are missing because Johnson switched phones in May 2021 following a “security breach”, but Hallet’s ruling now states that Johnson is providing them to the inquiry separately. It had been alleged that officials were struggling to unlock the old phone as Johnson had forgotten its password.

In August, openDemocracy revealed that the Cabinet Office had made a request for the Covid inquiry to hand back some of the evidence it had submitted. Hallett has allowed the request in respect of the evidence she deemed irrelevant herself, meaning it will not be formally presented to the inquiry.

The Cabinet Office has faced criticism since the start of the inquiry process for its attempts to block access to Johnson’s WhatsApp messages and diaries, with bereaved families calling the actions “outrageous”.

Hearings for the second module of the inquiry, which will examine decision-making during the pandemic, begin next month.