Trailer brake control system

A vehicle brake system comprising:

• a source of pressurized hydraulic fluid;
• a hydraulic service brake system having at least one service brake fluid circuit configured to forward a service brake demand of an operator;
• a trailer brake control system for connection to a trailer drawn by a vehicle, the trailer brake control system having a trailer brake valve which comprises:
• a brake demand input port;
• and
• a trailer brake demand output port for connection to a trailer brake control coupling, the trailer brake valve configured to generate a hydraulic fluid pressure output at the trailer brake demand output port which is dependent on the fluid pressure applied at the brake demand input port;
• and
• an electronic trailer brake control system including a control valve operative to fluidly connect the source of pressurized hydraulic fluid with the brake demand input port, the electronic trailer brake control system being operative in use to selectively supply pressurized hydraulic fluid indicative of a brake demand for the trailer to the brake demand input port.