Thanks for the welcome and the advice.
You are right about the checks I have done. We have a 4-car powerbase. The scalextic is 'Digital Supercars with 2 x Bugattis, so I think it is the basic 4 car powerbase.
You will need to follow the instructions that come with your digital set or powerbase to do this.
Are you refering to holding the button until it flashes twice as this is what it advises to do if you want to register the car with another controller.
So to clarify, both controllers can control one of the cars (when registered to that controller, independantly of course), no controllers have any input to the other car. "nd car is dead on track but first carcan be controlled with either controller.