not likely to be any risk whatsoever in this case. The police would unlikely prosecute them directly requireing a statement. What will likely happen is they will put an information marker on the car about anti social driving etc and they will get pulled by every ANPR cop car because of the flag on the system

People who drive like that usually make a habbit of being dicks so chances are if he hasnt got a section 59 then next time he is seen acting odly then he will get a section 59 rather than the chance of an officer using discretion with a verbal warning. if hes got a section 59 then next time he's pulled he will loose his car