Free range poultry and birds must be returned to fenced-in enclosures from today as the government declares an Avian Influenza Prevention Zone across the whole of Great Britain because of rising bird flu cases.

The country is currently facing its biggest ever outbreak with 190 confirmed cases and numbers still rising rapidly both among wild birds and on commercial premises.

With winter migration likely to drive numbers up further, as avian flu circulates naturally in wild birds and when they migrate to the United Kingdom from mainland Europe they can spread the disease to poultry and other captive birds, a decision has been made for the need for all bird keepers to follow strict biosecurity measures by law from this lunchtime to help protect flocks.

This will include keeping free range birds within fenced areas, minimising movement and contact around enclosures and fencing off standing water such as ponds.

Keepers with more than 500 birds will need to restrict access for non-essential people on their sites, workers will need to change clothes and footwear before entering bird enclosures and vehicles will need to be cleaned and disinfected regularly to limit the risk of the disease spreading.

Backyard owners with smaller numbers of poultry including chickens, ducks and geese must also take steps to limit the risk of the disease spreading to their animals.

In a joint statement the Chief Veterinary Officers for England, Scotland and Wales said: "Bird keepers have faced the largest ever outbreak of avian flu this year and with winter brings an even more increased risk to flocks as migratory birds return to the United Kingdom.

"Scrupulous biosecurity and hygiene measures is the best form of defence, which is why we have declared an Avian Influenza Prevention Zone (AIPZ) across Great Britain, meaning that all bird keepers must take action to help prevent the disease spreading to more poultry and other domestic birds.

"The introduction of an AIPZ means regardless of whether you keep a few birds or thousands, you are legally required to meet enhanced biosecurity requirements to protect your birds from this highly infectious disease."

The nationwide prevention zone builds on restrictions currently in place in some parts of the country, including Essex, Suffolk and Norfolk, where rising cases have prompted additional restrictions for keepers in those affected counties.

Earlier this month the NFU also raised concerns that Christmas turkey stocks could be at risk if cases were to spread among flocks in the run up to Christmas - a problem chairman of the NFU Poultry Board James Mottershead suggested could cause 'holy carnage'.

The new prevention zone means bird keepers in Great Britain, by law, must:

* Keep free ranging birds within fenced areas, and that ponds, watercourses and permanent standing water must be fenced off (except in specific circumstances e.g. zoo birds).

* Clean and disinfect footwear and keep areas where birds live clean and tidy;

* Minimise movement in and out of bird enclosures;

* Reduce any existing contamination by cleansing and disinfecting concrete areas, and fencing off wet or boggy areas

* Keep domestic ducks and geese separate from other poultry.

* Ensure the areas where birds are kept are unattractive to wild birds, for example by netting ponds, and by removing wild bird food sources;

* Feed and water your birds in enclosed areas to discourage wild birds

The risk to the public, says the UK Health Security Agency is low and poultry and eggs remain safe to eat. But walkers, including those out with dogs, are being advised to not touch any dead birds they find when out and about and instead report them by calling the Defra helpline on 03459 33 55 77.