I submitted the following query to The Police National Legal Database
(PNLD)

----------------------------------------------
If a passenger in a car opens a door and knocks a cyclist off their
bike -
can the driver of the car be prosecuted for this action of the
passenger.
Who would be prosecuted - and with what offence?

(The passenger is an adult with full mental faculties)

---------------------------------------------------
They have replied as follows:

Judith

Regulation 105 of the Road Vehicles (Construction and Use) Regulations
1986 creates an offence of opening a vehicle door so as to injure or
endanger any person. This would lend that individual who opened the
door being prosecuted at court. If it could be shown that the driver
also initiated the opening of that door s/he too could be prosecuted
for the same offence.

The Police National Legal Database (PNLD)

-------------------------------------------------------------------------------------

NB If it could be "shown" that the driver "also initiated the opening
of the that door"

As expected no mention of the driver being held responsible for the
action of the passenger unless the driver was also to blame and this
could be shown.