if a group of people littered out of their car, were told to pick it up by the litter picker man and then threw it out their car as they drove off, would the litter picker man be able to get them in trouble as he got their numberplate?

This stems off from a debate i had with a mate earlier as we saw a group of youths do this at the reservoir and we were arguing wether they could get in trouble for it or not. Anyone know?