Four dog breeds are banned, but cross breeds can be as dangerous
The Dangerous Dogs Act needs to be changed to focus instead on owners keeping aggressive dogs as a status symbol or weapon, the RSPCA has said.
It says the current Act is too vague and has led to an increase in dangerous dogs since it came into force in 1991.
It comes days after new guidelines were sent to police and local authorities.
The RSPCA wants more checks on owners and stiffer penalties for people mistreating dogs or keeping them for criminal use.
NHS figures showed the number of dog attacks had tripled since 1991, and many attacks have been blamed on cross-bred dogs which are not illegal.
In 2008, NHS figures showed nearly 3,800 attacks were taking place a year.
David Grant of the RSPCA said: "It's just a completely out of control situation ...my situation here in this RSPCA hospital is actually worse than before the Act came in."
Under the Dangerous Dogs Act four different breeds of dog are banned - the pit bull terrier, Japanese Tosa, Dogo Argentino and Fila Brasileiro.
But critics say the rules over what is a dangerous dog are too vague - even when it comes to identifying the banned breeds.
Dogs Trust veterinary director Chris Laurence told the BBC: "One of the big flaws in the Act is it doesn't tell you how to identify a pit bull.
NEW DOG GUIDELINES
Sets out best practice for the main enforcement authorities
Provides guidance on identifying pit bull terrier-type dogs
Provides examples of existing local initiatives
"You can actually breed a pit bull by accident. If you cross something like a boxer and a labrador or a labrador and a mastiff you end up with a dog that looks like a pit bull.
"The law says if it looks like a pit bull and the police accuse it of being a pit bull then it is a pit bull and it's up to you to prove it isn't."
Mr Grant said there were many incidences of dogs being abandoned and attacking other dogs, killing cats or attacking people.
On Friday the government rejected a bid to replace the Dangerous Dogs Act with a new law placing responsibility for a dog's behaviour on the owner or person in charge of it.
Lord Redesdale said, who proposed the replacement, said: "The Dangerous Dogs Act was a knee-jerk reaction to deal with pit bull terriers and was intended to lead to the extinction of that breed in this country.
"However research by the RSPCA has shown that there are now more pit bull terriers in the UK than there were when the Act was passed."
Dogs are being abandoned in record numbers, the RSPCA says
In south London, a council has already begun targeting dog owners for using dogs for intimidation, causing a nuisance, fighting with dogs or using them as a weapon .
"What we've done is introduce a registration scheme, linked to our tenancy conditions, which is going to promote responsible dog ownership, and take out sanctions on those people who aren't responsible who are causing a nuisance," said Mark Callis of the Dog Control Unit at Wandsworth Council.
"The ultimate sanction under our tenancy conditions would be eviction," he said.
In January, London's Metropolitan Police created a new unit to tackle the rise in the number of dogs being used by criminals.