Right I've done the following.
- Changed the control switch from a working golf, problem followed over.
- Disconnected the offside motor. Nearside motor worked when both the left and right selectors were moved.
- Swapped the motors over, the problem still follows, i.e. right still controls the left motor as well.
Not typically, if it was a problem with the individual motor I'd have thought that the fault would swap over, i.e. the right controls individually while the left controls both, which wasn't the case.
I've disconnected the battery and I'm going to let the car reset itself but it's not looking good