Boris Johnson said the Government must “smash on” and would “come out on top” in messages to his Cabinet Secretary as revelations of pandemic partying in Downing Street emerged.

The UK Covid-19 Inquiry was shown a WhatsApp exchange between the then-prime minister and his top civil servant Simon Case, who described the situation as “a bit grim.”

Counsel Hugo Keith said the messages, dated December 17 2021, were sent “around that time of the revelation of the partying in Downing Street”.

The whole business is insane. We will get through it and come out on top

Mr Johnson wrote: “I am really sorry this thing is now causing you any kind of grief at all.

“The whole business is insane.

“We will get through it and come out on top.”

Mr Case replied: “Thanks PM. It is a bit grim, but hopefully it will pass and I can get on with the real job I am supposed to do for you!”

Mr Johnson replied: “In retrospect we all should have told people – above all Lee Cain – to think about their behaviour in number ten and how it would look. But now we must smash on.”

Mr Cain was the No 10 communications director during the pandemic.

The first reports emerged towards the end of 2021 about parties, followed by a series of denials from Mr Johnson, Downing Street and Cabinet ministers.

On December 1 2021, Labour leader Sir Keir Starmer asked Mr Johnson why a Christmas party was thrown in Downing Street when millions of people were locked down.

“All guidance was followed completely in No 10,” Mr Johnson insisted at the time.

In April 2022, a No 10 spokeswoman confirmed Mr Johnson and then-chancellor Rishi Sunak would be fined for breaches of Covid regulations following allegations of lockdown parties in Downing Street and Whitehall.