Gassing badgers is "the most humane way" to control their numbers, Princess Anne has said.
The Government is considering introducing gassing after a report said that shooting the animals would not bring their numbers down enough to stop them spreading tuberculosis in cattle.
"If we want to control badgers, the most humane way of doing it is to gas them," the Princess Royal told the BBC's Countryfile programme.
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Among those expected to attend the ceremony will be former US President Bill Clinton and ex-Northern Ireland first minister Peter Robinson.
Five people have been killed and 40 injured after a car and knife attack in London on Wednesday.
A wet, wintry night in places with rain and hill snow slow to move away from southern Scotland and northern England.