The chairwoman of the UK Covid-19 Inquiry is expected to respond for the first time to a High Court challenge of her request for Boris Johnson’s unredacted WhatsApp messages.

Baroness Heather Hallett is due to hold a preliminary inquiry hearing on Tuesday in which she is set to address ministers’ decision to bring forward a judicial review.

The retired senior judge’s deadline for the UK Government to hand over the former prime minister’s WhatsApp messages and notebooks in an unredacted format was missed by the Cabinet Office last week, with ministers instead announcing plans to challenge the request in the courts.

It wouldn’t be appropriate for me to comment on this ongoing legal process

Cabinet Office minister Jeremy Quin looked to defend the move in the Commons on Monday, telling MPs that the High Court case would mean it was lawyers and not politicians who would decide “what is and what is not relevant information” for the inquiry.

Prime Minister Rishi Sunak has refused to comment on the row over Mr Johnson’s messages.

“It wouldn’t be appropriate for me to comment on this ongoing legal process,” Mr Sunak told The Daily Telegraph.

Mr Quin told MPs that he expected judges to hear the Government’s judicial review “very soon”, with a hearing “on or shortly after June 30”.

He denied accusations of a cover-up, saying that all Government correspondence relating to the handling of the coronavirus pandemic would be “made transparently available” to Lady Hallett’s investigation.

But he repeated the Cabinet Office’s argument that the inquiry, in its request for Mr Johnson’s unredacted WhatsApp correspondence and written notes, was asking for information ministers deemed to be “unambiguously irrelevant” and that had “nothing to do with Covid” decision-making.

Conservative MPs criticised the Government’s position, however, arguing it should be for Lady Hallett to decide what was relevant to her investigation.

Veteran MP Sir Edward Leigh said: “Let them have what they want and let’s get to the truth.”

Elkan Abrahamson, a solicitor representing the Covid-19 Bereaved Families for Justice campaign group at the inquiry, said the “only logical response” if chairwoman Lady Hallett does not get access to the material is for her to step down “because she can’t properly do her job”.

During Tuesday’s preliminary hearing, Lady Hallett is due to focus on Module 2 of the inquiry, which will look into core political and administrative decision making by the UK Government.

Preliminary hearings are for consideration of how the investigation should be run rather than taking evidence.

The first evidence session is due to take place next week, with Lady Hallett set to hear from witnesses about the UK’s pandemic preparedness and resilience as part of her Module 1 investigation.

Public hearings are scheduled to conclude by summer 2026, with interim reports published before then.

Lady Hallett hopes to publish reports for Module 1 and 2 next year, according to the inquiry’s website.