The government has been accused of an attempted “cover-up” as it bids to block the COVID inquiry’s request for Boris Johnson’s unredacted WhatsApp messages and notebooks.

Bereaved families and opposition parties criticised Prime Minister Rishi Sunak after the Cabinet Office revealed it was taking the unusual step of bringing a judicial review of Baroness Hallett’s order to release the documents.

It comes after Mr Johnson, the prime minister during the pandemic, said he was “more than happy” to adhere to the inquiry chairwoman’s request and hand over the material directly.

Ahead of a deadline of 4pm on Thursday to provide it, the Cabinet Office said it was bringing the judicial review challenge “with regret” and insisted it would “continue to co-operate fully with the inquiry before, during and after the jurisdictional issue in question is determined by the courts”.

The legal practice representing the COVID-19 Bereaved Families for Justice group, Broudie Jackson Canter, said the move showed “utter disregard for the inquiry”.

Labour’s deputy leader Angela Rayner accused the prime minister of “a desperate attempt to withhold evidence”.

“The public deserve answers, not another cover-up,” she added.

Liberal Democrats deputy leader Daisy Cooper said the government’s judicial review was a “kick in the teeth” for the bereaved families of the tens of thousands of people who died from COVID during the pandemic.

Read Adam Boulton’s analysis:
Politicians are drawn to WhatsApp – and it threatens us ever knowing the whole truth

The Cabinet Office’s argument is the documents and messages being sought by the inquiry are “unambiguously irrelevant” and cover matters “unconnected to the government’s handling of COVID”.

In a host of documents released as part of the legal proceedings, it emerged the WhatsApp messages given to the Cabinet Office by Mr Johnson are only from May 2021 onwards – more than a year after the pandemic began.

He was forced to change his mobile in 2021 after it emerged his number had been available online for 15 years.

The documents also included a list of 150 questions sent to Mr Johnson by the inquiry in February, including: “In or around autumn 2020, did you state that you would rather ‘let the bodies pile high’ than order another lockdown, or words to that effect? If so, please set out the circumstances in which you made these comments.”

He was also asked: “Between January and July 2020 did you receive advice from the then Cabinet Secretary that the Secretary of State for Health and Social Care, Matt Hancock MP, should be removed from his position? If so, why?”

A spokesman for the inquiry said more information about the Cabinet Office’s challenge would be provided at a preliminary hearing on 6 June.