As police raids see the arrest of three people for animal cruelty, the number of banned dogs used for fighting, then abandoned, is soaring.
In the pre-dawn gloom, a team of police and RSPCA officers wearing helmets, carrying stun shields and metal lassos gathered outside a door on a terraced street in central Birmingham.
With shouts of, "Police officers, open up, stay where you are!" they forced their way in.
At the end of the shabby back garden scattered with children's toys, they found a filthy pen, containing three dogs in cages. Two were banned pit-bull types, another was a Staffordshire bull terrier.
In a dark shed, leads, collars and a rifle hung on the walls, and a treadmill stood propped up on one end.
Vet David Grant: "There is no future for these dogs"
RSPCA Special Investigation Unit chief inspector Ian Briggs took photographs of everything, for evidence.
He said: "This is a normal treadmill, but they often adapt them for the exercise of dogs, building up their stamina prior to putting them in to an organised dog fight."
He pointed at a wooden pen that could be used to keep the dog on the runner.
"Organised dog fighting is a sophisticated act. It's very much like the training regime of a boxer - the dog has to reach a weight by a specific date," he said.
Pc Keith Evans, of the West Midlands Police dangerous dog unit, knelt down beside the wire as one of the dogs growled and wagged its tail.
"You can see the scars all the way down the front of the legs, around the shoulders, head, and muzzle, neck. That's where predominantly, the pit bull, when it's fighting, takes the most punishment," he said.
Other raids took place across Birmingham on Wednesday, leading to the arrests of three people on suspicion of animal cruelty, and the seizure of four dogs.
Pit bulls were one of the named breeds banned by the 1991 Dangerous Dogs Act, but the number being bred and crossed with other, legal breeds, including Staffordshire and English bull terriers, is on the rise.
One breeder said he earned £500 per puppy
Aside from being used in organised dog fights, they have grown in popularity as "status dogs" to intimidate others, taken out on the streets instead of a knife or a gun, for which the penalties are harsher.
The rate at which dogs of banned breeds are being seized in the West Midlands has doubled this year.
During the past 10 days, the BBC has met two breeders of pit bulls. One, who called himself Len, was unafraid to meet in a Birmingham park in broad daylight to show off three of them.
Their lithe, muscular bodies leapt several feet off the ground to catch the sticks he threw for them. "They are trained to jump at guns," he said.
He explained the largest of the three, a rich chestnut-brown bitch, was the mother of the other two. When the police raided his house, he kept the pregnant bitch hidden upstairs in the bedroom.
"The dog was downstairs. It bit a police officer and got put down. But they didn't find her."
He said he had bred the bitch three times so far, earning about £500 per puppy. He also described dog fights, held in the area fortnightly.
The other breeder, who gave his name as Gus, bought a four-month-old chocolate pit-bull bitch, destined to be a guard dog in a crack house.
He boasted of breeding top quality fighting dogs that could attract bets of thousands of pounds. According to Gus, demand was growing - there are not enough puppies to go around.
He said: "It's sort of a status symbol basically, having what's not allowed, what's illegal, having the biggest most vicious dog."
If pit bulls were legalised, he said, it would make a "huge difference" to how much money he could earn.
This is the worst it has ever been in terms of cruelty across the board; neglect, emaciated dogs, bad breeding, diseased dogs, fighting dogs
David Grant Vet
Asked if it would put him out of business, he replied: "Most probably."
At the RSPCA Hospital in Holloway, north London, vet David Grant had a busy waiting room, lined on one side with cages filled with howling dogs.
He said: "I worked here as a young vet in the early 70s. This is the worst it has ever been in terms of cruelty across the board - neglect, emaciated dogs, bad breeding, diseased dogs, fighting dogs."
Mr Grant said he had just had to put down a pit-bull cross. "She had been used as a breeding machine. They throw them out when they are tired and emaciated," he said.
He knelt down to pick up two hairless, puppies, which snuffled at his hands. Their skin was grey and scabrous. Pitbull-crosses, they had caught a type of mange from their mother that is easily treatable if caught early.
"I can't see one hair follicle on either puppy. This is the result of indiscriminate breeding. They will have to be put down," he said.
Dog homes say they are struggling to cope with the surge in the numbers of bull breeds being abandoned. Some 80% of those contacted by the BBC said they were being inundated with requests to house them.
One, in Buckinghamshire, said: "We are flooded out. If we opened our doors we could fill up with dogs of that type within an hour."
Another, in Wiltshire, said, "It's a massive problem. It's much, much worse than it was a year ago. These dogs are just getting slung out."
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.