Poultry on four new sites were ordered destroyed as a precaution to prevent the spread of the virulent H5N1 strain, after it was discovered Sunday on a farm with about 5,000 turkeys, 1,000 ducks and 500 geese.
A total of 24,000 turkeys were being slaughtered on the five sites, all connected to the Gressingham Foods company, according to the Department of Environment, Food and Rural Affairs. The agency said it was investigating whether H5N1 had spread between the sites.
Despite the fresh slaughter, all of the country's major supermarkets said the area under scrutiny accounted for just a small proportion of turkey supplies.
Bird flu's return to Britain — weeks before the Christmas holidays — was yet another blow to Britain's farmers, already struggling after livestock herds were hit earlier this year by foot-and-mouth and bluetongue.
The strain was closely related to those found in the Czech Republic and Germany earlier this year, Chief Veterinary Officer Fred Landeg said.
Millions of birds worldwide have died or were slaughtered since late 2003, when H5N1 began ravaging Asian poultry stocks. It has killed at least 206 people worldwide since 2003.
Experts believe most victims were probably infected through direct contact with sick birds.
Bird flu is difficult for humans to catch, but experts fear it could mutate into a form that spreads easily among people, potentially sparking a flu pandemic.