even if you dont claim it will affect you policy price, never report if you have no details of the other car if it is small damage, if you report it to the Police they will give you a crime number for the Insurance company. Dont give them that unless the Police find any evidence of the offender. seems stupid but thats life.
Insurance companies will usually set up a claim if you ring to report an incident as this is how they go about logging the information. Tell them that you don't intend claiming for the first incident and then they will close it off with no payment. They shouldn't then take this incident into account when calculating your premium but you can always ask them whether they have or not.