Baroness Hallett, the chair of the inquiry, has threatened the Government with legal action if it refuses to comply with her order for full copies of Mr Johnson’s communications and diaries, and the messages of a key aide, with a deadline of 4pm on Thursday to fulfil her demand.

But last night, Whitehall sources indicated that Mr Sunak would stand firm and refuse to submit unredacted material, from him or any minister, to the inquiry.