I suppose you have to ask yourself why he didn't stop? It could be perfectly innocent of course or he could have been reluctant to stop for a whole variety of reasons - he could have been drinking, he may not be taxed/insured or he may have done similar stuff and be known to the police.
I would call into my local police station and have a chat and let them decide if it's worth looking into further.
I would call into my local police station and have a chat and let them decide if it's worth looking into further.