Tyre Rubbish on the roads M25 in particular

Having had the 'pleasure' of a return trip on the M25 today I would love to know how all these huge tyre parts, some still circular some as long strips

A) come to be there, thankfully I have never witnessed one come spinning??? off, has anyone had this unfortunate experience? 

B) how do they end up either against the central reservation, in some cases standing upright, or on the verge?  Does some some stop and move them??  DANGEROUS, or do they make their own way to their resting places as they leave the vehicle they were attached too?

C) what is the vehicle that they were attached too left with?? Rims?? do they swerve or carry on it a straight line??

Sorry if I appear ignorant, but it has always fascinated me and today there seemed to be loads probably 20-30 in the 80 mile stretch on our return.  Couldn't say about on the way out as torrential rain and heavy spray.  Mind you that didn't stop people, including HGV's of all nationalities, closing braking distance gaps, moving sideways, and exceeding the variable speed limits.  But that should be another thread.

Thank for indulging me