A plea has been issued for backyard poultry keepers to take immediate action, amid a warning they could harbour a highly infectious strain of bird flu.

It is vital Cumbrians who keep a few hens or geese in their back garden to keep them indoors, or separate them from wild birds for 30 days following an outbreak of bird flu in Europe.

Fears have heightened in the county with the Solway Firth home to thousands of migrating birds over the winter.

National Farmers Union (NFU) Cumbrian council delegate Alistair Mackintosh said: "My concern is not the big egg producers. They will do what needs to be done and have the tools to do it.

"We have a lot of backyard poultry boys with half-a-dozen to 100 poultry. They could be harbouring the disease and not know it.

" They need to take this order very seriously. The last thing we want is the disease to get into these small keepers' poultry.

"I have a few hens myself, and brought them inside immediately the order was issued on Wednesday," he added.

A particularly virulent strain of avian influenza is killing large numbers of birds, and a source said that within the last day or two the virus has reached Calais.

It is the first time a warning to keep all poultry and captive birds indoors has been issued in the UK following an outbreak of bird flu.

David McCrea, a vet with Capontree Veterinary Practice in Brampton, said: "We don't have control over migrating birds, but we do have control over our poultry flock, whether big operations or small backyard keepers.

"Cumbria has a lot of people with a dozen birds in their backyard. They have names, they have an identity. But they must take every precaution they can to keep their poultry away from wild birds.

"Biosecurity is vital. A good disinfectant for footwear, refreshing it often. Keeping food and water away from wild birds and vermin."

He added: "If anyone detects illness in their birds contact their vet as a matter of urgency. We do not want a flock outbreak in Cumbria. I f our big producers lose tens of thousands of birds, it could potentially lose them their livelihood. "

Julie Smaile of Poultry Matters, a small family-run business based near Wigton, said she has had numerous telephone calls from worried poultry keepers asking what action they should take. She herself has had to house 300 birds.

"The problem is to keep them from becoming bored. They are free-range. They could turn on each other, which would be fatal for our business," Mrs Smaile admitted.

"Our sheds are wild-bird proof, and we will be taking the necessary biosecurity measures. There are no restrictions on poultry movement, so we can still continue our business of selling birds . I am just grateful it wasn't in the summer when we had thousands of birds on the ground, and no way of housing them all," said Mrs Smaile ."

Farmer Susan Aglionby, of Croft Farm at Aglionby, is a small poultry producer and described the situation as a "nightmare".

She has 26 hens and 28 geese, and has no sheds big enough to house them all.

"I have erected netting over our run to prevent wild birds getting in. I will be taking in their water and food to avoid contamination, and all our visitors will have to wear clean boots and use our disinfecting bath for their footwear," she explained.

"We have to take all the precautions we can. We are vulnerable in Cumbria because of the numbers of migratory birds that come here in winter. Our birds are free-range and they will be miserable, but better that than lose them to the virus."

David Brass, of The Lakes Free Range Egg Company at Stainton, said the disease was knocking at this country's door from all sides.

"It will increase our workload keeping them inside, but this strain is more virulent than we have had before," he said. " We have been lucky in the UK only having the odd outbreak. Biosecurity is easy for us, but not so for anyone with a few hens in the back garden."

The Chief Veterinary Officer has declared a Prevention Zone to introduce enhanced biosecurity requirements for poultry and captive birds in England that will remain in place for 30 days.

No cases of H5N8 have been found in the UK and this order is a precautionary measure to help prevent potential infection from wild birds.

Defra is continuing to monitor the situation closely and has increased its surveillance activity.