Rather than being billed by the rental company indirectly, I received 2 separate speeding tickets from 2 separate Australian provinces directly to my address in the UK, with credit card payment details. They were persuasive enough implying that if I had any intention of ever setting foot in Australia again, and did not want to be treated as a felon, it would be in my best interest to pay up...

Unless we are talking about an astronomical amount, isn't it worth just paying up? Who knows if, or where this can escalate...