Scientists are trying to determine the source of an outbreak of bird flu, which has lead to more than 160,000 turkeys being destroyed at a Bernard Matthews farm in Lowestoft, Suffolk.

Over the weekend, Defra confirmed the H5N1 strain of avian flu had been discovered at the farm.

A three-kilometre protection zone and a 10km surveillance zone have been set up around the site, while a wider restricted zone covering 2,090 sq km of east Suffolk and south east Norfolk has also been enforced.

Scientists are unsure how the birds contracted the virus, although it is most likely to have been spread by wild birds.

The virus is also the same as one found last month in Hungary, where an outbreak was discovered among geese.

“It's a complete mystery to us. We have the highest biosafety standards of anyone. We are waiting for Defra to finish its investigations and they will tell us the likely cause,” a spokesman for Bernard Matthews told the Guardian.