The update issued by Sue Gray’s team of investigators revealed that they examined emails, WhatsApp messages and text messages to establish “extensive substantive factual information”.

In January, it emerged Mr Johnson blamed “security issues” for not sharing relevant WhatsApp messages with Lord Geidt, who was conducting an independent investigation into the refurbishment of the Prime Minister’s flat.

This led some to question why his change of number meant the messages could not be found, as the platform offers advice on preserving messages in these circumstances.

Ms Harrison said WhatsApp groups focused on the coronavirus response were conducted on ministers and advisers’ private phones, because the pandemic required “remote working and fast-paced communications”.

The Government insists these were only used for “informal discussions”, and that all relevant actions “were copied across to formal channels and the official record where appropriate”.

Ben Jaffrey, representing All The Citizens, told the High Court that the use of private channels did not allow for “scrutiny through inquiries or court proceedings”.

But government lawyers argued that WhatsApp messages were only used for “informal” conversations, akin to those in a work corridor.