Dogs are used as "weapons" in areas plagued by gun and knife crime
Dangerous dogs bred illegally are being sold to strangers in London pubs for about £250, an MP has said.
Martin Linton, Labour MP for Battersea, said many of the dogs, mostly pitbulls and Staffordshire bull terriers, were trained to be used as weapons by gangs.
Surveys by Battersea Dogs and Cats Home, south London, show that one in 20 dogs admitted there were bought in pubs and most have to be put down, he said.
He called for tough new laws, including a minimum age for dog ownership.
The number of dangerous dogs in London has gone up in recent years, with the animals being used as weapons - to intimidate or attack - by gangs, police have said.
Between 2002 and 2006, the Metropolitan Police picked up 43 "weapon" dogs and last year the force said it was on target to remove more than 1,000 such animals from the streets.
Mr Linton said: "Certainly for Battersea Dogs and Cats Home it is a big problem because nearly half of the dogs they take in now are Staffordshires or other bull breed crosses.
"They have done surveys to show that at least one in 20 of these dogs is bought from a complete stranger in a pub.
"Nearly half of these are bought from unofficial breeders and the puppies change hands for about £250.
"Some people do re-home them, but in many cases it's impossible to re-home them and they have to be put down."
Mr Linton called for stricter registration and a minimum age of dog ownership as he claimed some teenagers wanted dangerous dogs as "status symbols".
"In order to protect the dogs themselves from being bred in very bad conditions we also need a system for compulsory microchipping for dogs because so many of them are used for intimidation in a crime as weapons."
The Battersea animal shelter suggested a minimum age of 18 for all breeds and 21 for those owning bull breeds and guard dogs.