Watch: Why has Sir Keir Starmer gone into coronavirus self-isolation?
The Labour leader will remain in isolation while awaiting the results of a test on the member of his household, a spokesperson said on Monday.
“This morning Keir Starmer was advised to self isolate after a member of his household showed possible symptoms of the coronavirus,” a spokesman for Sir Keir said.
“The member of his household has now had a test. In line with NHS guidelines, Keir will self-isolate while awaiting the results of the test and further advice from medical professionals.”
The situation emerged shortly after he took part in a show on LBC, and the Labour leader's office has alerted the broadcaster.
Sir Keir shared a studio with host Nick Ferrari during the phone-in show.
He will now continue working from home, but will not take part in Commons proceedings on Monday.
Prime minister Boris Johnson posted a message of support on Twitter on Monday following the announcement that Sir Keir had gone into self-isolation.
“I’ve spoken with @Keir_Starmer to pass on my best wishes. Sincerely hope he & his family are well,” Johnson wrote.
During his LBC appearance, Sir Keir said he supported the government's "rule of six" restrictions which have come into force this week.
He said: "I think you need something simple, easily understood and I think the government was slow back in February and March to appreciate the problem it was about the face and we can't repeat that error again, so I do support the 'rule of six'.
Watch: How is coronavirus treated?
"We've publicly come out in support of it and I will say, as I said to the prime minister I would, as the leader of the opposition I say to everybody, please follow the government advice, please follow these rules."
He added: "You can make the argument of why not five or why not six or seven – you have to go with a number backed by the science and they say six and I think we should abide by that rule."
Sir Keir said ministers' "side of the bargain" was to improve NHS Test and Trace and to ensure more people were self-isolating now that fresh social restrictions had been put in place.
Coronavirus: what happened today