Dangerous for me to get over involved here but Roberts' "old" Aero was being sold (now sold) by its current keeper because it is not raw enough (too good if you wish) and will be replaced by a traditional car.
To quote section 4 "Use" in the Super Sport Pedal Car Instruction book:
"Braking should be achieved by applying force in the opposite direction to normal pedalling. The handbrake should only be used when stationary and is not designed to slow the car when in motion".
Having said that, Robert should have had the car returned to him with the handbrake functioning for which I will take some responsibility.
George from RPM is now getting in touch with Robert to resolve this.