British DOG MASSACRE 1939 - why the Brits killed their dogs in WW II?

In 1939, British pets were killed by their owners, the majority of them were dogs. Why did it happen? The eventis called as British Pet Massacre, or British Pet Holocaust and not many people know about it. Why the Brits decided to kill their dogs (and cats)? British dogs in war in the homeland. Dogs in war documentary!