Nadine Dorries with Boris Johnson. She felt unwell on Friday but went on to hold a surgery for 50 constituents the next day Andrew Parsons/i-Images Picture Agency

More than 100 people including Boris Johnson, his fiancée Carrie Symonds, two cabinet ministers and Dame Kelly Holmes were at a Downing Street reception that was attended by Britain’s first MP to contract coronavirus.

Nadine Dorries, 62, a health minister, went to the International Women’s Day reception in Downing Street on Thursday last week, the day she first started to show signs of the virus and was beginning to feel “a bit peaky”. She was formally diagnosed last night.

Liz Truss, the international trade secretary, and Anne-Marie Trevelyan, the international development secretary, were also both at the event.

Anyone who has spoken directly to someone with coronavirus or stood near them for prolonged periods will be contacted by health officials and told to self-isolate if…