As many as 450 British citizens remain unaccounted for in Japan following an earthquake and subsequent Tsunami last Friday.
The Foreign Office fears ten are dead, whereas there are serious concerns about 50 more British citizens in the country.
It is believed a further 400 will have survived, although they are likely to be hungry and homeless, the Foreign Office added.
An FCO spokesperson said: “It’s highly likely that between eight and 12 Brits are dead.
“They are in the affected areas and can’t be found.
“There are serious concerns for about 50 others but they still may be found.”
There are around 17,000 British nationals living in Japan, with around half being based in Tokyo, 150 miles from Fukushima where a fire has now broken out in reactor number 4 after three plant explosions.
A further 300,000 British holidaymakers arrive in Japan each year.
The Foreign Office is, however, presently advising against all but essential travel to Tokyo and northern Japan following the incident last week.