Panorama's Tom Heap follows two Staffordshire bull terriers - Ska and Brandy - as they are tested by staff at Battersea Dogs and Cats Home to see if they are suitable to be offered out for adoption to find them new homes.
Battersea has released new figures showing that about a third of the dogs they take in have to be put to sleep. Most of them are healthy animals but they are deemed to be unsuitable for rehoming. Animal charities such as Battersea say the problem is on the rise and is in part a reflection of a growing street trend for aggressive-looking "status" dogs.
Panorama: Britain's Unwanted Pets, BBC One, Monday, 2 August at 2030BST.