If you start seeing a grren marker near the rear indox mark of a vehicle or trailer

then this is why.

New SI amendment marker just published : Now you know lecky ahead?

he purpose of this instrument, which amends the Road Vehicles (Display of Registration Marks) Regulations 2001 (S.I. 2001/561) (“the 2001 Regulations”) is to introduce into the 2001 Regulations the legal requirements for a new optional feature of displaying a green background on the left-hand side of a registration plate for eligible vehicles with zero tailpipe emissions, as a means of identifying those types of zero emission vehicles.