SO, can someone please refer me to the section of law regarding my rights to get rid of them?
I understand it isn't as simple as shooting them, but I'm still unclear on what I can and cannot do and I can't find the law online.
Simple answer, the owners are under no obligation to do anything. You are not permitted to trap them, move them (they're regarded as property so thats theft) or otherwise harm them.
Welcome to a no win situation.
Options (depending on how you feel about these):
1. Talk to owners about distress/killing of childrens pets and ask them to contribute to costs for better cages etc (good luck)
2. Get one of those water sentry things
3. try one of the many fabled fixes (tiger ****, orange peel, starfish). I've got a vet mate who sniggers when any of these are mentioned.
4. 1 large supersoaker filled with a dilute mix including chilli oil. Aim for eyes/****. It works as a detterent.
5. If they're not tagged, remove them and hand into RSPCA. You won't be thanked.
Personally I like my garden to be a haven for natural species, not some introduced predator that kills indiscriminantly.