Dangerous dogs are widely available to buy on the internet, a BBC Radio Five Live investigation has found.
Four breeds of dogs, including pit bulls, are banned
The probe found more than 100 websites advertising pit bulls and other breeds banned under the Dangerous Dogs Act.
The animals were on sale for between £300 and £1,000. One seller described his dog as being "like a loaded gun".
Former Conservative Home Secretary Lord Baker told the BBC the Kennel Club was watering down the law by placing blame with owners not dogs.
Lord Baker, who introduced the Dangerous Dogs Act in 1991, said it was "absolutely ridiculous" to give ASBOs to dog owners rather than accept that certain dogs were dangerous by nature.
"The act should now be fully implemented to ensure we are safe from pit bull terriers and pit bull terrier types - these dogs that are bred to kill," he said.
But Caroline Kisko, secretary of the Kennel Club, said the peer's remarks were "completely inaccurate" and insisted pit bull terriers were not naturally more aggressive than any other breed.
'Kill a child'
Five Live found illegal dogs being bred and fought across the UK and recorded conversations with sellers who described the violent nature of their dogs.
One said: "It's just like having a loaded gun."
Another said: "He can really do some nasty work. He's got the strength to kill a child, basically, no problem."
"If anyone comes into your garden, they're not walking back out," a third said.
Sellers also described methods of smuggling the dogs into the UK, for example by hiding them in the back of a horsebox.
When Five Live later confronted them, most denied any wrongdoing and some said they were no longer involved in the sale of banned animals.
One said: "I think you'll find what I said was, 'It can be done', but I don't deal with that any more."
Chief Inspector Mike Butcher, from the RSPCA's special operations unit, told Five Live he had witnessed the aftermath of many dog fights.
"Obviously you have a pit, lots of blood, two dogs, appalling injuries - the dogs very rarely survive their injuries," Mr Butcher said.
"The people that attend these dog fights are normally people that have a liking for violence, often have previous convictions for violence, drugs, firearms, so obviously the police come with us, and they normally accept a prison sentence quite easily."
Many of the sellers Five Live spoke to were from Birmingham.
Labour MP for the city's Perry Barr constituency Khalid Mahmood said it was "disgraceful and shameful" that people were selling dangerous dogs and organising fights.
He said he believed ownership was increasing in the Asian community as a symbol of "street cred".
"It seems to be a badge of honour to be able to have these sort of dogs," Mr Mahmood said.
Caroline Kisko said the Kennel Club wanted to tighten the law to make people more responsible for the behaviour and training of their dogs.
Ellie Lawrenson was killed by a pit bull terrier-type on New Year's Day
"This is not an issue of dogs, this is an issue of people," she said.
"Can you imagine if you go into a West Highland White or any other dog and you beat it regularly, you set it on other dogs, right from the word go, right from when it's a puppy, you encourage aggression.
"What do you think is going to happen? You're going to have a highly aggressive West Highland White."
Since 1991, it has been against the law to advertise, breed or sell four breeds of dangerous dog - pit bull, Dogo Argentino, Fila Brasileira and Japanese Tosa.
The RSPCA said it would investigate evidence gathered by Five Live and seek prosecutions if appropriate.