It is the sixth time the Holborn and St Pancras MP has been forced into isolation since taking the top job after being a close contact with a Covid case or catching the virus himself. His most recent quarantine is the second time he has caught the virus after last being infected with Covid in October 2021.

       On that occasion he returned a positive test on the day of the Budget, meaning he was unable to deliver Labour's response to Rishi Sunak's plans for the economy.

       His latest isolation will come as another blow to Sir Keir who had been hoping to use the turn of the year to reboot his beleaguered leadership.

       Labour has been boosted in the polls in recent weeks as public frustration with the Government mounts, but there has been little uptick in support for the party's leader.

       On Tuesday, Sir Keir addressed an audience in Birmingham as he sought to seize the week to make the case for a Labour government.

       He promised "straight leadership" based on the values of "security, prosperity and respect" if his party is returned to power.

       The Labour leader said: "I have a very clear idea of what a Labour government would look like.

       "And in 2022 I want to take my plans to the British people."

       Sir Keir is not thought to have any Covid-19 symptoms but the infection was picked up as part of his regular testing routine.

       Ms Rayner traded blows with Mr Johnson at PMQs once before the last time her boss was in isolation.

       On that occasion she was credited with making the Prime Minister squirm as she probed accusations of Tory sleaze.

       More to follow...