(Bloomberg) -- Former Prime Minister Boris Johnson said he would provide copies of his Covid-era WhatsApp messages directly to the country’s inquiry into the pandemic, undercutting Rishi Sunak’s effort to block their release. 

The Cabinet Office said on Thursday it was asking a court to review the request for unredacted documents by Heather Hallett, the retired judge appointed by the government to lead the inquiry. But Johnson — who had previously handed the WhatsApps over to the Cabinet Office — told Hallett in a letter on Friday that he would also give them directly to her.

“While I understand the government’s position, 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,” Johnson said in the letter, which was provided by his office.

The former premier’s actions are a challenge to Sunak, who served as Johnson’s Chancellor of the Exchequer until resigning last year and helping to precipitate his downfall. Sunak’s refusal to hand over the requested material in an unredacted form has sparked opposition party accusations of a cover-up, given that Johnson’s correspondence will include messages exchanged with his former chancellor.

Sunak’s government has said the material is “unambiguously irrelevant.” 

While Johnson had previously said he would hand all his pandemic-era WhatApp messages to the Cabinet Office, on Thursday the government said that the material includes diaries and WhatsApp messages covering only the period from May 2021. 

Messages before that — a period which covers the first Covid lockdowns and the initial response to the pandemic — are contained on a mobile phone that Johnson says he was advised by security services never to switch on again. In Friday’s letter, Johnson said he would like to hand that material over also — but that he needed to “test” the advice of the country’s security services that he could no longer access the old device “safely.”

“I have asked the Cabinet Office for assistance in turning it on securely, so that I can search it for all relevant material,” he said. “I propose to pass all such material directly to you.”

Johnson said in his letter that he had no access to his pandemic notebooks any more, because they’re now held by the Cabinet Office. He said he had asked it to forward the notebooks to Hallett, and that if they declined to do so, he would request their return and then provide them directly to her.

©2023 Bloomberg L.P.