A bird flu prevention zone has been declared across the whole of England, as more dead wild birds were found with the virus.
The move, announced by the Government's chief veterinary officer Nigel Gibbens, means all poultry and bird keepers in England have to follow strict measures to protect their livestock from the disease.
It comes as 13 dead wild birds were confirmed to have the virus in Warwickshire, following the discovery of the disease in wild birds in Dorset, where a total of 31 infected birds have now been identified.
A local prevention zone was put in place in Dorset, which has now been extended to the whole of England.
Testing of the birds in Warwickshire is ongoing but it is thought they had the H5N6 strain of the virus which has been circulating in wild populations in Europe in recent months, and which is deadly to birds.
But officials said it was a different variant of H5N6 from the one which affected people in China last year, and the risk to public health was very low.
The Food Standards Agency said bird flu does not pose a food safety risk for UK consumers.
The prevention zone means keepers must ensure areas where birds are kept do not attract wild birds, for example by netting ponds, and feed and water their livestock in enclosed areas to discourage contact with wild birds.
They must also minimise movement in and out of enclosures, clean and disinfect footwear and keep areas where birds live clean and tidy, and reduce any existing contamination by disinfecting concrete areas and fencing off wet or boggy spots.
But the prevention zone does not mean that birds must be kept inside, and there are no plans for movement restrictions or culls at the moment.
Prof Gibbens said: "Following the latest finding of bird flu in wild birds in Warwickshire, we are extending our action to help prevent the virus spreading to poultry and other domestic birds.
"Whether you keep just a few birds or thousands, you are now legally required to meet enhanced biosecurity requirements and this is in your interests to do, to protect your birds from this highly infectious virus."
Keepers with more than 500 birds have to take extra measures including restricting access for non-essential people, changing clothing and footwear before entering bird enclosures and cleaning and disinfecting vehicles.