Bird flu experts are waiting to hear whether the deadliest strain of the virus has struck with fatal consequences for the first time on Europe's doorstep.
Tests are being conducted at the Veterinary Laboratory Agency in Britain, on samples of the avian flu virus which killed a brother and a sister on a farm in Turkey .
One other family member and seven other people in eastern Turkey are in hospital with suspected bird flu.
The key questions are whether the latest outbreak involves the feared H5N1 strain of the flu - and whether it has fulfilled scientists' fears and mutated into a disease transmissible between humans.
Results from the Weybridge tests are expected in a few days.
However, experts insisted today there was no evidence of a mutation. Professor Hugh Pennington, president of the Society of General Microbiology, said: "This (outbreak) shows we have to keep our vigilance up but the picture, as far as the human population is concerned, hasn't changed.
He added: "It's still an avian virus and hasn't mutated to enable human-to-human infection.
"So the message is: don't panic.
"The public shouldn't be unduly concerned. We can all do our bit to keep bird flu away from these shores. If you see a dead bird, stay well away from it and report it immediately to a vet."
The latest outbreak comes on top of the 142 confirmed cases in south-east Asia in the last two years, including at least 70 deaths.
There have been no deaths so far outside south-east Asia from the deadly H5N1 strain.