You must tell your insurer about ANY 'accident'. Within a specified time frame which is usually 48 hours or as soon as praticable. To clarify police only need to ATTEND if the road is blocked or there are injuries. For your own good however you should report each and every 'accident' to the police and get a log number for it.

I would always go through insurance. I didn't one time and it bit me in the arse and cost me a crap load of money!