It came as calls grew for the material to be handed over by Thursday’s 4pm deadline, as the government continued to signal it would resist the demand from inquiry chair Baroness Hallett.
Mr Johnson’s team is said to be preparing to hand over WhatsApps and notebooks directly to the inquiry if the chairwoman comes to him for the evidence.
Sir Jonathan Jones, the government’s former legal chief, told The Independent that the “cards are stacked” against the Sunak government if the increasingly “bizarre” dispute goes to court.
“It’s a mess,” said the senior KC. “It’s likely the court will have to rule on it – it doesn’t seem either side is minded to back down. I’m not aware of any precedent for the government refusing to give information to a public inquiry it set up. It’s all pretty extraordinary.”
He added: “The powers of a public inquiry are wide. There is logic to the position the Covid inquiry is taking – that it has to see the material to decide on its relevance. The cards are stacked in favour of the inquiry. The bar for getting a court to strike down a request is high.”
Former Supreme Court justice Lord Sumption also said attempts to withhold the messages were likely to fail – saying he did not think the Cabinet Office’s arguments would “cut much ice” in the courts.
Lord Sumption said that under the law the “ultimate judge” of whether the material ought to be disclosed was the inquiry chair. “I frankly can’t see the courts quashing her decision,” he told the BBC’s World At One.
Arguing that going to court would be a “political mistake”, he added: “They are not going to succeed in a judicial review so that all they will achieve in resisting is to make it look like they are hiding something.”
Sir Jonathan said that if the Sunak government refused to hand over the Johnson material by the deadline, the Covid-19 inquiry has two options.
Baroness Hallett’s team could either go to the High Court to seek an order from a judge – or launch a criminal lawsuit by arguing the government’s refusal to provide information violates the Inquiries Act 2005.
In her recent exchange of letters with the Cabinet Office, the chairwoman pointed out that failure to comply could be a criminal offence and punishable with a fine of up to £1,000 or even imprisonment for a maximum of 51 weeks.
“Presumably [the Covid-19 inquiry] would try to hold some senior figure in the Cabinet Office responsible,” said Sir Jonathan on the possibility of criminal proceedings, before describing the scenario as “extraordinary” and “the least likely outcome”.
The ex-Treasury solicitior said it was “quite likely” the government will seek a judicial review before Thursday at 4pm to “test the validity” of Baroness Hallett’s request.
Urging a rethink, Sir Jonathan said: “It would be quite a climbdown for the government to say it will provide information, but I think it should consider doing so to avoid extreme scenarios.”
The row risked descending into farce when Mr Johnson said he was happy for his messages to be given to the Covid inquiry – only for the government to say it did not have the unredacted messages any longer.
An ally of Mr Johnson told The Independent he was “happy” to provide with the Covid inquiry with the material it wants, but was currently being blocked by the Sunak government.
The PM’s team has told Politico that he would be prepared to hand over requested messages and notebooks if asked directly by the inquiry, and was readying the material via his new solicitors.
But No 10 has said that while there is nothing to stop Mr Johnson handing any personal evidence directly to the inquiry, any “government-owned” material would need to be disclosed by the government.
The Covid inquiry would not be drawn on whether it could ask and accept material directly from Mr Johnson, if Thursday’s deadline passes without a climbdown from the Cabinet Office. A source said the inquiry would “cross that bridge if it comes to it”.
Former Tory cabinet minister Malcolm Rifkind told The Independent Mr Johnson should be allowed to hand over his WhatsApps messages. “If he’s willing to that he should be able to do so. It’s his WhatsApp messages – not theirs [the Cabinet Office].”
Mr Rifkind also said a compromise could still be reached – suggesting that the government and Lady Hallett agree on a “independent” broker to look over the messages and decide what should be redacted.
With the deadline looming and Mr Sunak facing accusations of a “cover up”, work and pensions secretary Mel Stride insisted that the government had “nothing to hide”. Mr Stride told Sky News claiming the inquiry already has “all the information that it is right for it to have”.
However, senior Tory MP Caroline Nokes said the “reluctance” by the government to provide the WhatsApps and notebooks “seems a nonsense”. She told Talk TV that it would be “less pain for the government if they hand [the material] over quickly”.
Senior Tory William Wragg, chair of the public administration and constitutional affairs committee, also urged the government to back down. “If the inquiry requests documents and info – then whoever it has asked should comply,” he told the BBC.
Labour’s shadow health secretary Wes Streeting has said Mr Sunak looks “really slippery” over the refusal to hand over requested files. “One minute the government says the messages they have are immaterial; the next minute they’re saying they don’t exist. Which is it?”
Historian Sir Anthony Seldon, who has chronicled Mr Johnson’s time in No 10, said it was a “simple no-brainer” for the messages to be handed over. “This event was so seismic and the premiership of Boris Johnson was so catastrophic, we have to get out the full facts,” he told TalkTV.
Meanwhile, a Johnson ally told The Independent the ex-PM should sue the Cabinet Office for the recent referral to the police over possible fresh Covid rule breaches at Chequers at No 10.
“If I was Boris I would go legal and flush out any cover ups,” they said. “I think the plotters have overplayed their hand in trying to destroy Boris and their actions are beginning to unravel.”
The Independent has approached the Cabinet Office and Mr Johnson’s office for comment.