Keir Starmer will be self-isolating after one of his children tested positive for Covid.
The announcement came shortly after the Labour leader appeared in the Commons chamber for prime minister’s questions on Wednesday.
It will be the fourth time he has had to enter quarantine since the pandemic began.
A spokesperson for Starmer said: “One of Keir’s children tested positive for Covid this lunchtime.
“In line with the rules, Keir and his family will now be self-isolating.
“Keir was already doing daily tests and tested negative this morning. He will continue to take daily tests.”
During PMQs, several Conservative MPs sat in a tightly packed group, many not wearing face coverings, while social-distancing was observed by the Labour benches.
Boris Johnson is already self-isolating after coming into contact with health secretary Sajid Javid, who has tested positive.
The PM took part in PMQs virtually from his country retreat of Chequers.