A relative of a UK patient who recently contracted a potentially fatal Sars-like virus has also become infected with the disease, health experts said.
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.
University Hospitals Birmingham NHS Foundation Trust said it was treating a patient who presented to staff on Saturday night and was being treated for novel coronavirus.
The hospital said the patient was initially given care in a single room on a ward, where stringent infection controls were put in place, and was allowed a limited number of visitors.
Their condition deteriorated on Sunday and they were moved to an isolation room in critical care, where they are now described as "stable".
A hospital spokeswoman said: "The patient did not come into direct contact with any other patient.
"All staff treating the patient complied with relevant infection control policies, wearing masks, gowns and gloves.
"The patient's condition is stable."
She added the room was being "cleaned daily with detergent and hypochlorite" and visitors were having to wear masks and gowns.
The trust said the patient was an existing out-patient "undergoing treatment for a long-term complex and unrelated health condition" which means they have a weakened immune system, making them susceptible to infections.
The hospital spokeswoman added six hospital staff who had come into close contact with the patient were being monitored but had not displayed any symptoms so far.
"The hospital is working closely with the Health Protection Agency," she said.