The breeding, sale and exchange of pit bull terriers is banned
The number of illegal dogs on the streets is rising according to the Metropolitan Police, with the RSPCA warning that young men are using vicious breeds as weapons of intimidation and status symbols.
Gordon Shepherd, 25, a part-time DJ from Shepherd's Bush in west London, owns a pit bull and Rottweiler crossbreed called Rocky.
He says he likes it when he is out with Rocky and people are scared of them.
"People move out of the way. I've walked down the street, and people literally move. That makes me feel, like, yeah, I've got power."
And people have good reason to be frightened. Gordon admits he has trained Rocky to bite anyone he points out "straightaway".
"Sometimes you just have to beat it into them, so they have to do it. If you're going to actually train your dog to be violent, that's [when] you would actually hit it into him, to actually be violent," he says.
Gordon is well aware that his dog could cause serious damage.
"[It's] just as good as having a knife - the damage that that could do to a person if used in the right way."
And it is not just people that are potential victims. The RSPCA says dogs are increasingly being used in street fights, resulting in dogs having to be treated for stab wounds, burns and broken bones.
Marlon, who works with young people who are involved in gangs, thinks dogs are also becoming a big part of gang culture.
"They may feel like they're not the strongest person so they get themselves a strong powerful dog," he says.
Akel Isaac (right) bred his French mastiff dog to earn some extra cash
Akel Isaac, another young dog owner from Wandsworth, says image plays a big role in dog ownership: "Having a dog is all about how you get seen."
Akel recently bred his huge French mastiff dog, Krueger, with another French mastiff, to earn some extra cash. He says the puppies were in demand even before they were born.
The 19-year-old thinks there is an increasing demand for bigger and more aggressive dogs because there is a status dog culture.
"You do see a lot of big dogs nowadays but they're still crossed with Staffs or pits or some type of fighting dog, cause [the owners] still want to keep that characteristic in there - so that they're easy to train when it comes to attacking people."
Up until 18 months ago the status dog breed of choice was Staffordshire bull terrier.
They gained a reputation for aggression which many responsible owners say they do not deserve. But now Staffordshire terriers have fallen out of fashion, and are being replaced by even bigger, stronger breeds.
Whereas breeding French mastiffs is legal, the Dangerous Dogs Act 1991 bans the breeding - and cross breeding - of four types of fighting dogs in the UK, including pit bull terriers.
The Act was introduced after some particularly vicious attacks on members of the public, and the idea was that as a consequence, the pit bull and other aggressive breeds would die out.
But that has not happened.
Sergeant McParland, head of the new dedicated Metropolitan Police Dangerous Dogs Unit, says there is a growing problem of illegal dogs on the streets.
"In the year 2002-2006 the Met seized around 40 dogs a year, but all of a sudden in 2006 we started seeing an increase in the numbers of pit bull terriers in London. The numbers went up to 173 that year, to 480 the following year, and in the last ten months we've seized well over 600 dogs."
A big part of the problem is identifying which dogs are pit bulls.
There are only a few police officers who can definitely identify pit bulls, and cross breeding is making it harder for the authorities to crack down on all kinds of illegal dogs because it is more difficult to identify them.
Weighing up options
Sergeant McParland acknowledges there are tens of thousands of status dogs in London alone, but says the new unit "will not patrol the street sweeping pit bulls off the streets". The Met Police simply does not have the resources.
But he believes 90% of the problem is not the dogs - but the owners at the end of the leash.
The RSPCA is calling for the government to review current dog legislation to place more responsibility on owners.
Gordon Shepherd is not sure whether his dog Rocky is legal. But he says when the police did ask him about his dog he was able to fob them off.
"I've only ever been stopped once with them asking what breed of dog he was. That's when I lied. I said he was a Staff and a Labrador."
But he realises, irrespective of whether a dog is legal or illegal, owning a potentially dangerous dog could result in the law being broken.
"If you was to be the owner of a dog, and that dog was to kill someone, the sentences ain't that big," he says.
"I've thought of the consequences afterwards, the possibility of being arrested and sometimes if you weigh up your options, it's possibly better to let the dog bite the person than your life could be ended."
My Weapon Is A Dog will be shown on BBC Three at 2100 BST on Thursday 21 May.