Not sure exactly when they changed but I noticed new plastic trolleys in Dickson today. I have my doubts that entirely replacing a fleet of salvageable metal trolleys with plastic ones (even if recycled plastics) is actually "pushing for a greener future".
I can't see these being usable as long as a metal trolley could be, particularly as trolleys spend a decent amount of time in sunlight. A few years of UV exposure is hard for plastics to stand up to - I've noticed with the recycled plastic picnic tables that the older ones are fading and starting to get crumbly on the exposed surfaces.