Health minister Nadine Dorries has said she has been diagnosed with coronavirus.
The Tory MP, who is thought to have mixed with hundreds of people at Westminster in recent days and was at a Downing Street reception attended by Boris Johnson, fell ill on Friday.
The 62-year-old, who represents Mid Bedfordshire, has been self-isolating since receiving the diagnosis.
She tweeted on Wednesday night that she was “over the worst of it” and was worried about her elderly mother, who had developed a cough.
It comes as a sixth person died from the virus in the UK, which has a total of 382 cases.
The latest man to have died was in his 80s and is thought to have had underlying health conditions.
Dorries said in an official statement: “I can confirm I have tested positive for coronavirus.
“As soon as I was informed I took all the advised precautions and have been self-isolating at home.
“Public Health England has started detailed contact tracing and the department and my parliamentary office are closely following their advice.
“I would like to thank PHE and the wonderful NHS staff who have provided me with advice and support.”
The ally of the PM’s was one of the key figures in drawing up legislation in dealing with the outbreak in the crucial last few days.
Health Secretary Matt Hancock tweeted: “Really sorry to hear Nadine has tested positive for coronavirus. She has done the right thing by self isolating at home, and both NHS and PHE staff have been brilliant. We all wish her well as she recovers.
“I understand why people are worried about this disease. We will do all we can to keep people safe, based on the best possible science.”
A number of people also wished the Conservative minister a speedy recovery after the news emerged on Tuesday night.
Others, including independent candidate for London mayor Rory Stewart, reiterated calls for more action.
It comes as chancellor Rishi Sunak prepares to unveil the government’s budget on Wednesday, with emergency funds for the NHS, workers and businesses to help the country cope with the contagion set to form the central plank of the announcement.