A savage pit-bull attacked a collie dog puppy in Normand Park, prompting borough MP Greg Hands to raise the issue of dangerous dogs in Parliament.
The terrifying attack, which happened in the Fulham park last week, left the young dog badly injured and needing expensive veterinary treatment.
And to make matters worse, it is understood the pit bull's owner then launched a volley of abuse at the collie's shaken keeper, who was with her young child.
Mr Hands says the shocking incident is a further example of the government's failure to successfully deal with the issue and raised his concerns during Home Office questions.
He said: "I wasn’t there at the time, but a resident emailed me this week to tell me of an awful attack by what was described as a pit-bull attacking a puppy in front of it’s child owner’s eyes.
"With toddlers of my own, I can tell you this sort of thing can be a horrifying experience. The puppy was badly injured and will require I am told more than a thousand pounds of veterinary treatment. The dangerous dog’s owner became abusive to those who complained, and even swore loudly at the mother of the grief-stricken toddler.
"The Government has launched an already failed scheme of compulsory insurance for dogs. This will add a lot of cost and bureaucracy for existing dog owners, while doing nothing to stop those bent on getting round the law (illegal dogs will, after all, be uninsurable).
"Instead what we need is a new approach of much tougher sentences, of the sort we would expect for those with knives or other weapons, and we need to make the police’s job easier by allowing them to deal with incidents on the spot, rather than having to always taker the dog into kennels, at some expense."
Hammersmith and Fulham Council says confiscating illegal dogs is a priority and claimed it has one of the best records in London in tackling the problem, seizing 59 dangerous canines in 2008-2009.
It puts its record down to Operation Bark, a joint venture between the council, police RSPCA and the Mayhew Animal Home.
Teams make monthly patrols in areas where there are suspected problems.
Suspected dangerous animals can be seized by the police and taken to kennels, until expert dog handlers decide if they are dangerous and fall under one of the four banned breeds in Britain - the pit bull terrier, Japanese tosa, dogo Argentino and fila Brasileiro.
The case can then come before a magistrates' court, which can order the dog be micro chipped, wear a muzzle or that only someone over the age of 16 can walk the dog. The maximum penalty for owning a banned dog is a fine of £5,000 and six months in prison.
To report a banned type dog in the borough, call 020 8753 1081 or email email@example.com.