* Man was flown from Qatar to UK hospital
* Case "unlikely to prove concern", experts on alert
* U.N. health body investigating
By Kate Kelland
LONDON, Sept 24 (Reuters) - A Qatari man struck down with a previously unknown virus related to the deadly SARS virus and the common cold is critically ill in hospital in Britain, the World Health Organisation said on Monday.
The United Nations health body said it is urgently seeking more information about the new virus, which comes from the same family as the SARS virus that emerged in 2002 and killed 800 people.
Peter Openshaw, director of the Centre for Respiratory Infection at Imperial College London, said the virus was unlikely to prove a concern, but experts would watch out for any sign of it spreading.
The 49-year-old patient has symptoms of an acute respiratory infection and kidney failure, the WHO said, without giving details of which hospital he was staying in.
"The patient is still alive but, as we understand, in critical condition," Gregory Hartl, spokesman for the Geneva-based WHO, told Reuters.
"We are still investigating this. We're asking for information from whoever might have seen such cases, but as of the moment we haven't had any more notifications of cases."
The WHO issued a statement late on Sunday through its "global alert and response" system saying tests on the Qatari man had confirmed the presence of a new, or novel, coronavirus.
"Given that this is a novel coronavirus, WHO is currently in the process of obtaining further information to determine the public health implications," the statement said.
Coronaviruses are a large family of viruses which includes the common cold and SARS.
SARS, or Severe Acute Respiratory Syndrome, appeared in China in 2002 and infected more than 8,000 people around the world, killing around 800 of them before being brought under control.
The WHO said the Qatari patient had gone to the doctor on September 3, 2012, suffering from the symptoms of an acute respiratory infection. It did not say in which country the diagnosis was made.
On September 7, he was admitted to an intensive care unit in Doha, Qatar and on September 11, the man, who had also recently been in Saudi Arabia, was transferred to Britain by air ambulance from Qatar.
It did not say why the ill man had been moved to the UK.
"The Health Protection Agency (HPA) of the UK conducted laboratory testing and has confirmed the presence of a novel coronavirus," the WHO said.
It said scientists at the HPA compared gene sequences of the virus from the Qatari patient with samples of virus sequenced by Dutch scientists from lung tissue of a fatal case earlier this year in a 60-year-old Saudi national.
The results showed a 99.5 percent identity match, it said.
Openshaw said the fact the two cases found so far are apparently unrelated suggests "that what has been picked up is just some rare event that in past times might have been undiagnosed".
But he added: "Any evidence of sustained human-to-human transmission or of contact would be more worrying, raising the worry that another SARS-like agent could be emerging." (Reporting by Kate Kelland; Editing by Andrew Heavens)