The Cabinet Office tried to object to handing over the communications but was overruled by Baroness Hallett, the chair of the COVID inquiry.

But the inquiry chair has ordered that the release of unredacted WhatsApp messages and diary entries from the former prime minister.

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The order was first made last month, but the Cabinet Office appealed it.

Downing Street insisted the government was supplying "all relevant material" to the inquiry.

The Cabinet Office has already provided more than 55,000 documents, 24 personal witness statements and eight corporate statements to the inquiry.

But the government believes it has no duty to disclose "unambiguously irrelevant" material, according to the Cabinet Office in its initial objection.

Lady Hallett disagrees, and under the Inquiries Act 2005 has the final word.

In her response to the government, the chair rejects their argument about them deciding what or what isn't "unambiguously irrelevant".

She said in her ruling that all these documents "contain information that is potentially relevant" to how decisions were made during the pandemic.

Mr Johnson wrote to the inquiry claiming that he was not the one to blame for the redactions, and that the order "may directly and/or indirectly suggest that I have failed to provide documents to the Inquiry".

He added: "Any such suggestion or implication would be unfair and untrue."

Writing in a letter dated 24 May, he asked for at least a 48-hour to delay the publication of the order, so he could seek legal advice.

He also revealed that he is currently changing his legal team.

The inquiry did not grant this delay and published the order the same day - although they released the letter from Mr Johnson alongside their announcement.

Within her reasoning, Lady Hallet states as an example that messages between Mr Johnson and his advisers about the Metropolitan Police's handling of the Sarah Everard protests were initially assessed by the Cabinet Office to be "unambiguously irrelevant" to the inquiry.

Redacted copies were then supplied, and these have since been unredacted.

Lady Hallett says this was "not a promising start".

She also identified communications - which have still only been seen in their redacted form - that the chair considers are "in fact relevant to my investigation".

The way in which WhatsApps were used to form policy between the UK and Scotland is listed as an example.

A spokesperson for COVID-19 Bereaved Families for Justice UK said it was "outrageous" the government "think they can dictate to an independent inquiry which of Boris Johnson's WhatsApp messages they can see".

"With the revelations that have come out yesterday about him breaking lockdown rules, you really do fear the worst about what they're hiding."

Labour's deputy leader, Angela Rayner, said: "The fact the COVID Inquiry has had to invoke legal powers to compel the handover of crucial documents suggests that this is a government with much to hide.

"Rather than fighting legal battles to withhold evidence, it is essential that ministers now comply so the public is able to get to the truth and those responsible can be held to account."