The Cabinet Office is seeking a judicial review of Baroness Hallett’s order to release Boris Johnson’s WhatsApp messages, diaries and notebooks, it has said in a letter to the COVID inquiry.

The Cabinet Office, in a letter to the inquiry, said it was bringing a judicial review challenge “with regret” – but added that there were “important issues of principle at stake”.

It said it would “continue to co-operate fully with the inquiry before, during and after the jurisdictional issue in question”.

The government has so far refused to hand them over in their entirety to the official inquiry – and the deadline to do so expired at 4pm today.

Inquiry chair Lady Hallett ordered the government to hand over the documents last week – without any amendments.

The tranche includes messages sent between former prime minister Mr Johnson and his fellow ministers and advisers during the pandemic, as well as diary entries.

On Wednesday afternoon, Mr Johnson’s team said all the information the inquiry wanted had been passed to the Cabinet Office.

His spokesman said the ex-prime minister wanted the Cabinet Office to “urgently” hand over the material.