A duck farm in Norfolk and a backyard flock in Dorset are two of the latest premises impacted by avian influenza this winter, Defra has confirmed.
Highly-pathogenic bird flu of the H5N8 subtype was found at a commercial duck breeding premises near Attleborough, Breckland, Norfolk on 20 December.
All ducks, around 8,000, will be humanely culled, Defra said in an update on the growing avian influenza situation impacting the UK this winter.
A 3km Protection Zone and a 10km Surveillance Zone have also been put in place around the farm.
In a separate outbreak on Saturday 19 December, high-path avian influenza H5N8 was confirmed in backyard poultry near Gillingham, Dorset.
All birds on the premises will be humanely culled, and a 3km Protection Zone and 10km Surveillance Zone have been declared.
Last week, the government confirmed two other cases of bird flu, at a poultry farm in Orkney and a backyard flock of chickens in North Yorkshire.
The increasing number of cases comes as mandatory housing measures were rolled out across the country from the start of this week.
It is now a legal requirement for all farmers and poultry keepers to keep their birds indoors following a string of outbreaks.
They will need to follow strict biosecurity measures to limit the spread of avian influenza and eradicate the disease.
The risk of incursion of bird flu is 'very high' for wild birds, and 'medium' for poultry with high biosecurity and 'high' for poultry with poor biosecurity.
A joint statement from Britain’s three Chief Veterinary Officers (CVOs) said: "Whether you keep just a few birds or thousands, from 14 December onwards you will be legally required to keep your birds indoors.
"We have not taken this decision lightly, but it is the best way to protect your birds from this highly infectious disease."
How can I prevent bird flu?
Keepers are advised by Defra to be vigilant for any signs of disease in their birds and any wild birds, and seek prompt advice from their vet if they have any concerns.
They can help prevent avian flu by maintaining good biosecurity on their premises, including:
• Housing or netting all poultry and captive birds
• Cleansing and disinfecting clothing, footwear, equipment and vehicles before and after contact with poultry and captive birds
• Reducing the movement of people, vehicles or equipment to and from areas where poultry and captive birds are kept
• Thoroughly cleaning and disinfecting housing at the end of a production cycle
• Keeping fresh disinfectant at the right concentration at all points where people should use it, such as farm entrances
• Minimising direct and indirect contact between poultry and captive birds and wild birds, including making sure all feed and water is not accessible to wild birds