Supermarkets could face a shortage of turkeys this Christmas as tests are carried out on a farm in Suffolk where the turkeys are understood to have contracted avian flu.

The H5 strain of the virus was detected by preliminary tests after turkeys at the farm fell ill. The farm supplies supermarket giants Sainsbury’s, Somerfield and Budgens.

A protection zone has been set up around the farm and a statement issued by the Department for Environment, Food and Rural Affairs (Defra) said preliminary tests showed it was the H5 strain, but it is not yet known whether it is H5N1, which killed about 200 people worldwide.

All turkeys are being slaughtered at the farm and Defra will investigate to find out what other measures need to be taken.

The National Farmers’ Union poultry board chairman Charles Bourns said turkey supplies over Christmas would not be affected and the cull was equivalent to only a small proportion of the 10 million turkeys sold at Christmas each year.

Earlier this year, bird flu was found at a Bernard Matthews turkey farm in Suffolk.