The UK government also said on Monday that the outbreak was a "serious and imminent threat" and announced new measures to protect the public.
However, it should be remembered that according to Public Health England, the actual risk to individuals remains just "moderate", and that it was necessary for the Government to make this declaration so it could forcibly detain people suspected of having the virus.
Evacuees were taken to Kents Hill Park for 14 days of quarantine.
It has killed more than 900 people, majority in China, and has spread to at least 27 countries and territories.
Most people have only mild symptoms such as fever and runny nose.
All came into contact with him while his was in France.
Two infections in a Hong Kong apartment building sparked an evacuation
The unnamed man, who has since been quarantined, has been linked to a total of seven other cases, including one in France and Spain. More than 440 cases have been confirmed outside mainland China, including two deaths in Hong Kong and the Philippines.
As the death toll in China from the virus rose to 811, Prof Whitty said: "A further patient has tested positive for novel coronavirus in England, bringing the total number of cases in the United Kingdom to four".
The apparent ease with which virus spread raises concern that some of the 90 others who attended the conference may also have been infected and "may go on to initiate chains of infection in their home countries, " said Dr. Nathalie MacDermott, a clinical lecturer at King's College London.
Britain issued its "imminent threat" declaration after a British man who caught the virus in Singapore in January appeared linked to several other confirmed cases in Europe.
"Public Health England is contacting all passengers who were seated in the vicinity of the customer on flight EZS8481 from Geneva to London Gatwick on 28 January to provide guidance in line with procedures". The airline said it was notified by Public Health England (PHE) on the evening of February 6, with all 183 passengers now being contacted.
Health Minister Katsunobu Kato said the Japanese government is considering testing all 3,711 passengers and crew on the Diamond Princess.
More than 900 people have died and 37,000 have become infected since the outbreak began in the Chinese city of Wuhan, which has been placed in lockdown to curb the spread - an evacuation flight landed at RAF Brize Norton yesterday.