Boris Johnson is "running rings" around Rishi Sunak by directly handing over unredacted WhatsApp messages to the independent public inquiry investigating the UK's response to coronavirus, a former Number 10 adviser has claimed.
The ex-Prime Minister, who appointed Sunak as his Chancellor in February 2020, revealed he is sending the probe his messages from May 2021 onwards.
Johnson also wants to pass on WhatsApp messages from his old phone but the device can no longer be accessed safely.
A former Number 10 adviser, who worked alongside Johnson, told GB News: "This was a fight that didn't need to happen.
A former Number 10 aide suggested Boris Johnson is 'running rings' around Rishi Sunak
"Boris is running rings around Number 10 on this.
"It's out of retaliation, it's not Boris picking the fight."
GB News understands that the Government's decision was made yesterday and not in response to Johnson's recent statements.
The Cabinet Office has also stressed that the public inquiry does not have the power to disclose such information and fears that handing over the messages could set a dangerous precedent for Government policy and individual privacy.
The ex-Prime Minister previously sent the relevant information to the Cabinet Office but it refused to comply with the inquiry's order to have over all the material in unredacted form.
The Government instead pursued an unprecedented high court judicial review over the Covid inquiry's request to release Johnson's messages, diaries and notebooks.
Boris Johnson voluntarily handed over his unredacted messages
A judge will have to decide whether the inquiry has overreached its legal powers in a potential showdown in court.
Johnson, whose political career remains at risk from the Privileges Committee's separate investigation into Partygate, penned a letter to Lady Heather Hallett.
He said: "I am not willing to let my material become a test case for others when I am perfectly content for the inquiry to see it.
"I am therefore providing the material directly to your inquiry today in unredacted form."
Johnson added: "I am sending your inquiry all unredacted WhatsApps I provided to the Cabinet Office.
"I would like to do the same with any material that may be on an old phone which I have been previously told I can no longer access safely.
Rishi Sunak (left) and Boris Johnson (right)
"In my view of the urgency of your request I believe we need to test this advice, which came from the security services."
The ex-Prime Minister also claimed he has approached the Cabinet Office for assistance in securely accessing the relevant material and asked the department to pass on his notebooks.
Responding to Johnson's statement, former Work & Pensions Secretary Esther McVey said on GB News: "I am intrigued to see the WhatsApps because I want to see how informal formal decisions were made."
The Government missed yesterday's 4pm deadline to share Johnson's messages and notebooks.
Organisations representing bereaved families and opposition MPs condemned Sunak for failing to comply with Dame Hallett's request.
Boris Johnson faces a separate probe about whether he misled Parliament
Elkan Abrahamson, the lawyer representing the COVID-19 Bereaved Families for Justice group, said: "The Cabinet Office is showing utter disregard for the inquiry in maintaining their belief that they are the higher power and arbiter of what is relevant material and what is not.
"It raises questions about the integrity of the inquiry and how open and transparent it will be if the chair is unable to see all of the material."
Labour's deputy leader Angela Rayner labelled the legal challenge as a "desperate attempt to withhold evidence"
She said: "While the rest of the country is focused on the cost-of-living crisis, Rishi Sunak is hopelessly distracted with legal ploys to obstruct the Covid inquiry in a desperate attempt to withhold evidence.
“After 13 years of Tory scandal, these latest smoke-and-mirror tactics serve only to undermine the Covid inquiry. The public deserve answers, not another cover-up.”
Angela Rayner slammed the Government for seeking a judicial review
The Liberal Democrats claimed the legal challenge was "a kick in the teeth for bereaved families who've already waited far too long for answers".
Deputy leader Daisy Cooper warned: "Rishi Sunak's promise to govern with integrity and accountability has been left in tatters.
"The Government is delaying the inquiry even further and clogging up court time, all to prevent Sunak and his Conservative colleagues from having to release their messages."
However, the Cabinet Office stressed it was launching court proceedings "with regret".
The Cabinet Office also insisted that Dame Hallett's demands would lead to an "absurd" scenario where "ambiguously irrelevant" material sent and received by ministers was shared.