A Cabinet minister has insisted the Government trusts the UK Covid-19 Inquiry chairwoman despite issuing a legal challenge to the retired senior judge’s request for information.

Health Secretary Steve Barclay said Baroness Hallett was a product of the UK’s “world-leading” judiciary.

But he said it was “right” that the ministers “test a legal aspect” when it came to the submission of WhatsApp messages relating to Government decision-making during the pandemic.

The Cabinet Office has started the process of a judicial review of Lady Hallett’s request for former prime minister Boris Johnson’s unredacted WhatsApp messages and notebooks.

The court will decide where the boundaries are, so that won’t be a decision taken by the Government

Mr Barclay, asked on BBC Radio 4’s Today programme whether he and Prime Minister Rishi Sunak trusted the inquiry chairwoman, said: “Yes, I do.

“I think we are extremely fortunate in this country with the quality of the judiciary and in particular in this case, so that is not in question at all.

“I think there is huge support for the inquiry, that is why the Government has set it up. For those who lost loved ones in particular, the inquiry is hugely important and the Government stands ready to fully comply with that inquiry.”

The decision to challenge the inquiry in the High Court is seen as highly unusual and even a minister has raised doubts that the Government will win the contest, which could be heard before the end of the month.

Mr Barclay defended the legal action, arguing that it was right to seek court instruction on the submission of WhatsApp messages as it was a “new area” in terms of the way Government business is carried out.

He said it would be judges rather than politicians making the ruling on whether the chairwoman should see Mr Johnson’s unredacted correspondence.

“The court will decide where the boundaries are, so that won’t be a decision taken by the Government,” he told Today.

“Wherever those boundaries are then set by the courts, then the Government will of course comply. And that is what the Cabinet Office is clarifying.”

The Cabinet Office says some of the information requested by the inquiry does not relate to the pandemic and is “unambiguously irrelevant”.

Mr Barclay told Sky News there were “issues in terms of people’s privacy and their wider rights in terms of what messages may be sent” to the national inquiry.

At a preliminary inquiry hearing on Tuesday, Lady Hallett questioned why the Cabinet Office would want to redact information that Mr Johnson has confirmed he is happy to submit.

She has given the department until the end of the week to clarify whether it would seek to redact information in Mr Johnson’s notebooks, his diaries and the WhatsApp messages on his locked mobile, containing messages dating from before May 2021, if they were obtainable before the judicial review is heard.

Former health secretary Matt Hancock has submitted his WhatsApp messages in an unredacted format, Tuesday’s central London hearing heard.

Mr Barclay, asked on LBC whether he will be doing the same, said he would “comply with whatever the inquiry requests” but that he would await direction from the courts regarding WhatsApp messages.

The first public evidence session of the inquiry is due to start on Tuesday, with witnesses being called to give testimony about Module 1 of the investigation which relates to the UK’s pandemic preparedness.