The relative of a UK patient who recently contracted a Sars-like virus has also become infected with the potentially fatal disease.
On Monday, the Health Protection Agency (HPA) said one person who had recently travelled to the Middle East and Pakistan was being treated in an intensive care unit at a Manchester hospital after becoming infected with a new type of coronavirus.
Now officials have confirmed that a relative of the patient, who is also a UK resident, has become infected and is being treated at the Queen Elizabeth Hospital, Birmingham.
It is understood that the family member, who does not have any recent travel history, has an existing medical condition that might make them more susceptible to respiratory infections.
The latest case brings the number of confirmed cases across the world to 11, three of which were diagnosed in the UK, the HPA said.
Last year British health officials identified another case of the novel coronavirus.
A 49-year-old Qatari man was treated at St Thomas' Hospital in London after becoming infected.
Health experts cautioned that the risk to the general population "remains very low".
Professor John Watson, head of respiratory diseases at the HPA, said: "Confirmed novel coronavirus infection in a person without travel history to the Middle East suggests that person-to-person transmission has occurred, and that it occurred in the UK.
"This case is a family member who was in close personal contact with the earlier case and who may have been at greater risk of acquiring an infection because of their underlying health condition.
"To date, evidence of person-to-person transmission has been limited. Although this case provides strong evidence for person-to-person transmission, the risk of infection in most circumstances is still considered to be very low.
"If novel coronavirus were more infectious, we would have expected to have seen a larger number of cases than we have seen since the first case was reported three months ago. However, this new development does justify the measures that were immediately put into place to prevent any further spread of infection and to identify and follow up contacts of known cases.
"In light of this latest case we would like to emphasise that the risk associated with novel coronavirus to the general UK population remains very low."
Five patients have died as a result of the infectious disease, none in the UK.
The HPA said there have been five cases confirmed in Saudi Arabia resulting in three deaths, while two patients treated in Jordan both died.
A patient from Qatar was treated in Germany but has since been discharged.
Infected patients have presented with serious respiratory illness with fever, cough, shortness of breath and breathing difficulties.
Coronaviruses cause most common colds but can also cause Sars (severe acute respiratory syndrome). In 2003, hundreds of people died after a Sars outbreak in Asia.
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