The Government will fight a legal battle over the Covid inquiry’s demand to release Boris Johnson’s unredacted WhatsApp messages, diaries and personal notebooks.

The Cabinet Office said it was seeking a judicial review of inquiry chairwoman Baroness Hallett’s order to release the documents, arguing that it should not have to hand over material which is “unambiguously irrelevant”.

In a letter to the inquiry, released after a 4pm deadline to hand over the material, the Cabinet Office said it had provided “as much relevant information as possible, and as quickly as possible” in line with the order.

But the letter said: “The Cabinet Office has today sought leave to bring a judicial review. We do so with regret and with an assurance that we will continue to co-operate fully with the inquiry before, during and after the jurisdictional issue in question is determined by the courts, specifically whether the inquiry has the power to compel production of documents and messages which are unambiguously irrelevant to the inquiry’s work, including personal communications and matters unconnected to the Government’s handling of Covid.”