Here’s a thing I don’t understand about dogs — bad dogs, I mean; dogs that look like canine wrestlers, with barrel-shaped bodies, squat little legs and horrible snarling faces. The thing I don’t understand is: why are they even around?

Why, every time I walk down a street or cross a park, do I come across at least one gang of teenagers egging their bad dog on, teaching it to attack trees or setting it after blameless passers-by for a joke?

Certain breeds of dogs can, and do, kill or maim people — we’re all familiar with stories on the news about “family pets” basically eating babies; the owner always looks astonished and says something like, “I just don’t understand what came over Satan; he’s normally good as gold”. The voiceover inevitably explains that Satan, or Killa, or whatever — was “immediately put down”, as though this were a terrible sadness instead of cause for celebration. My question is: why was Satan around in the first place — and why are his siblings ruining great swathes of our inner cities?

Last week a summit aimed at addressing the issue of the growing number of “weapon dogs” on London’s streets was held at City Hall. The number of suspected dangerous dogs seized by the Metropolitan police rose by 60% in the past year; court cases involving dangerous dog offences rose by 50% between 2006 and 2007. In the past five years London’s hospitals have seen admissions for dog bites increase by 79% (the national increase is 43%).

Kit Malthouse, the deputy mayor for policing, said urgent action was needed so that “Londoners are free to walk the streets without fear of a snarling weapon dog”. Too right and I expect the problem isn’t merely the capital’s: bad dogs are everywhere, especially in inner cities.

Also last week, my daughter was accidentally knocked over by some monstrous rottweiler-looking thing. She was fine, and the beast’s owner grunted a semblance of an apology, but it was one of those moments when, if I’d had a gun, there would have been carnage (that’s a terrible thing to say, but I’m afraid that in my advanced old age these moments occur quite frequently). The dog’s owner was 14 or 15. The dog looked insane but was neither muzzled nor on a lead. The dog, basically, was a weapon — they all are. They are the equivalent of walking around with a massive knife.

If I ventured out of the house with a massive knife, I’d be arrested and probably detained for psychiatric evaluation. If I walked out of the house with a bad dog, on the other hand, there’d be no problem, provided my dog was microchipped (and how are you going to tell — are you going to stroke the slavering fang-dog all over to feel for something the size of a grain of rice?).

I realise it’s not helpful to call bad dogs “weapon dogs” — if you’re a certain kind of person, the very words sound glamorous and hard and gangsterish, causing you to long for nothing less than a weapon dog of your own.

This is only a tiny generalisation, because I’ve observed these dogs’ owners for some years now and, in my experience, bad dogs are owned by insecure boys or young men who want to be hard and who therefore do hard-seeming things such as hang around in gangs. Tiresomely, some of them are genuinely hard and their gangs are real, which means you become wary of telling off bad dog owners. You just walk around feeling intimidated and taking detours through the park.

I can’t begin to express how furious this makes me. I was talking to a friend who lives near a little patch of green that is also a shortcut to her bus stop. She’s had to stop using it because the green has been colonised by teenagers and their dogs; when they’re not making the dogs fight, they’re standing around jeering as someone tries to mate the dogs (another thing I see about twice a week and one that, for some reason, is particularly disturbing — it just seems so disrespectful to the animals).

The green has benches, which people used to sit on with their newspapers; local mothers of young children used to use it as a spot in which to allow their toddlers to let off steam. No longer.

The RSPCA says that 60% of the calls it receives concern dog-fighting in the context of youths gathered in public places. Battersea Dogs’ Home says bull breeds account for 50% of its inmates.

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