Dont know if this helps, but here is Toronto's bylaw regarding reptiles, where it prohibits:
Crocodylia (such as alligators, crocodiles, gavials)
All snakes which reach an adult length larger than 3 metres
All lizards which reach an adult length larger than 2 metres.
All venomous and poisonous animals.
Also, here is Brampton's bylaw regarding:
No venomous reptiles
They do not seem to have a maximum length limit, but by banning all boids, they have automatically set a limit of 7-8 feet.
Just like Jeff H said, perhaps these bylaws would help you show that London's bylaws are too restrictive, I cannot think of many snakes that have an adult length of 2 feet.
Hope this helps.