I had an incident when a woman steamed past a Give Way traffic island while I was approaching and knocked my wing mirror clean off. We both informed insurance companies, but spoke later and she offered to pay for the new mirror glass, and mentioned that her insurance had gone up because she told her broker about the incident. However, I buy my insurance online, and most companies now only ask if you've had "Any claims or convictions in the past 5 years", of course I tick "No", because we never claimed.
I know of an elderly man whose bumper got badly scuffed while parked in Tescos, and the other driver left no details. He reported this to his insurance company, and even though he didn't claim, his premium went up significantly, because he was now considered "A higher risk".
I sometimes wonder why we bother with car insurance, the ones to don't have it (around 20-30% of us apparently) always get away with it. And any insurance company's solution to any incident is 50/50, to avoid using the legal cover we pay for. Ridiculous. At least we get free Tax-Disc holders...