THE UK is experiencing the “largest-ever outbreak” of avian flu, the Environment Secretary has warned.

It came as the UK’s chief vet said there is a “phenomenal level” of the disease in circulation following the culling of tens of thousands of farmed birds.

An Avian Influenza Prevention Zone was declared across the UK on November 3 before being extended on November 29 with the added requirement all captive birds had to be kept indoors, amid concerns that wild birds migrating from mainland Europe during the winter are carrying the disease.

There are 40 infected premises in the UK, according to chief veterinary officer Christine Middlemiss.

The risk to human health from avian influenza remains very low, according to public health advice, and there is a low food safety risk.

Speaking in the House of Commons, Tory Environment Secretary George Eustice said: “Each year the UK faces a seasonal risk in incursion of avian influenza associated with migratory wild birds. While we have that each year, I have to say this year we are now seeing the largest-ever outbreak in the UK of avian influenza with 36 confirmed cases.”

On the measures the Government is taking, he added: “We have put in place an avian influenza prevention zone that came into force on the November 3 in England and November 17 in Northern Ireland, and an additional housing order was introduced on November 29. Our chief veterinary officer continues to lead the response to this episode.”

Middlemiss told the BBC the “phenomenal level” of bird flu has “huge human, animal and trade implications”.

She said the disease is being spread by migratory birds flying back from the north of Russia and eastern Europe, and insisted further research is needed to prevent a worsening outbreak in the future.

“We can’t wait until another year and have an even bigger outbreak. So, we will be working not just with our own scientists but internationally, to understand more of what we can do about what’s behind it,” Dr Middlemiss told the broadcaster.

The vet warned the UK is only a few weeks into a migratory season that goes on until March.

“We are going to need to keep up these levels of heightened biosecurity for all that time,” she said.

Middlemiss told BBC Radio 4’s Today programme there are 40 infected premises in the UK – 38 in Great Britain including 33 in England, adding that around half a million birds have been culled so far.

The protection zone means that, in addition to keeping birds and poultry housed, keepers must continue to take precautions such as regularly cleaning and disinfecting clothing, equipment and vehicles and limiting access to non-essential workers and visitors.

Defra has said the new housing measures will be kept under regular review.