By Chris Smith
They're called "weapon dogs" or sometimes "status dogs" - animals like pit bull terriers, kept by gang members to intimidate, to attack, or to fight each other.
The Metropolitan Police's Status Dogs Unit was on its biggest raid yet
In an attempt to help ease the problem, the Metropolitan Police status dogs unit was formed in London earlier this year to seize and identify dangerous dogs.
Sergeant Ian McParland is head of the unit and explained how the dogs are being used.
He said: "The dogs are being used by gang members, or people on the periphery of gangs, to intimidate.
"They're being used for violence, they're being used for robberies. Almost every piece of crime you can think of, you can use a dog."
This morning the unit was out on the streets for its biggest operation yet.
Dog handlers wearing protective padded sleeves carried fire extinguishers and special poles to control dangerous breeds.
Twelve addresses were raided, and 20 dogs taken away.
They'll need to be tested, but the early signs are that they're all pit bulls.
A litter of six puppies were found and handed over to the RSPCA
At one house, officers broke down the door when they got no reply.
Dogs could clearly be heard inside and two adult pit bulls were taken away.
One had to be controlled by two policemen as it snapped and snarled in fright.
Upstairs, the unit found a litter of six puppies, which were handed over to the RSPCA.
Breeding pit bulls is banned under the Dangerous Dogs Act and many of the animals taken away have to be put down.
Sadly, that may happen to these puppies.
Ian McPartland says he's a dog lover, and most pit bulls are lovely animals.
He blames the owners for most problems with the breed.
He said: "Terrible. I spent 25 years as a dog handler and now I'm out there taking dogs off people who really don't know how to treat them.
"Their behaviour with the dogs is atrocious.
"I think most of my unit would agree that 90% of the problem is on the owner's end of the leash.
"But obviously when you've got something like a pit bull on the other end the potential for it going seriously wrong does rise."