lets say someone hit yr car when u r not around or hit yr car, b4 u could notice his license plate, he had gone out of yr sight....then u have no choice but to either pay for yr own damage if its small damage or lodge a report and have it claim under yr own damage claim...thus effecting yr NCD..
or
if someone bang yr car, and if its obviously he is at wrong, e.g jumping que, hazardous parking, bang yr rear or rear side of yr body, came out from junction etc etc ...and he refuses to pay, then u should copy his number plate and possible his road tax disc no. you cant insist to see his license or ic if he refuse to give u. u may snap a pics of the car with the surrounding. this might help in yr police report. try get his phone number.
if after 24hrs he dont lodge a report, the sarjan will call him or send him a notice(warrant) for him to make report. if he still don make report, then we need to seek the sarjan's help to issue an " accident plan" to prove he is wrong, then u may proceed to claim the other party insurance without losing yr ncd.