The Department for Environment, Food and Rural Affairs (Defra) said that a temporary control zone imposed on Friday at the affected farm has now been replaced by a 10 kilometre surveillance zone and an inner 3 kilometre protection zone.

The map of the protection and surveillance zones shows that the infected farm is just north east of Preston.

The laying hen unit in Lancashire is understood to involve a mixed 170,000 bird flock of housed and free range layers.

Restrictions remain in place and the humane culling of all birds at the farm is continuing.

The restrictions mean that all poultry farms within the 10 kilometre control zone around the infected premises are not allowed to move poultry, captive birds or other mammals except under licence.

The H7N7 virus is not the type of avian flu that caused the recent outbreaks in the US, which was the H5N2 variant of the disease. However, a case of low severity H7N7 avian influenza was found in Hampshire in February 2015.

Human infections with avian flu are rare, and the virus found in Lancashire is also not seen as a major concern for human disease. However, some viruses, such as H5N1 or H7N9, have been associated with human disease.

Chief Veterinary Officer, Nigel Gibbens said: "Final tests results have confirmed a case of avian flu at a farm in Lancashire.

"Restrictions put in place last week will continue and the humane culling of all birds at the site is progressing. These actions are part of our tried and tested approach to dealing with previous outbreaks.

"Public Health England has confirmed that the risk to public health from this strain is very low. The Food Standards Agency has said there is no food safety risk for consumers.

"Bird keepers should remain alert for any signs of disease, report suspect disease to their nearest APHA office immediately and ensure they are maintaining good biosecurity on their premises."

Defra reiterated its strong track record of controlling and eliminating previous outbreaks of avian flu in the UK. The outbreaks in Yorkshire last year and Hampshire in February were both successfully contained, allowing restrictions to be lifted at the earliest opportunity.

Andrew Large, Chief Executive of the British Poultry Council, said: “Action is being taken to contain the Avian Influenza and to prevent any possible spread. We are monitoring the situation closely. As ever, poultry farmers are urged to maintain high vigilance and bio-security.”

An investigation into the case is ongoing.