It is understood the Prime Minister met with a group of MPs for 35 minutes on Thursday morning which included Ashfield MP Lee Anderson who has since tested positive for coronavirus.
Johnson, who has already had Covid-19, was subsequently instructed to self-isolate by NHS Test and Trace. He is expected to continue speaking to the country during his self-isolation period.
Johnson credited his excellent hospital care - including a Kiwi nurse from Invercargill - for his recovery from the virus.
Anderson confirmed he tested positive in a Facebook post on Sunday night. He, and his wife developed symptoms on Friday and on Saturday, Covid tests confirmed they had contracted the virus.
"On Friday I lost my sense of taste at the same time my wife had a bad headache. I had no cough, no fever and felt well," Anderson wrote.
"We both had a test on Saturday and the result came in Sunday morning. My wife and I both tested positive.
"I feel absolutely fine and my biggest concern is my wife who is in the shielded group. But we are both feeling good."