The law states that a trailer with a maximum GVW of 750 kg (i.e. the maximum permitted mass), the trailer itself does not need to be braked (unbraked). This means that your towing car will slow down. If the GVW is 751 kg or more, the law states that the trailer itself must also have a braking system (overrun brake). This means that when the towing vehicle brakes, the trailer itself also brakes.
It is a fully autonomous system and requires no modification to your vehicle.