Vehicle Braking System

A vehicle braking system comprising a spring brake actuator having a spring brake chamber, a spring brake control assembly and an immobiliser valve which is movable between brake release position in which the spring brake control assembly is operable to cause the flow of pressurised fluid into the spring brake chamber or to vent the spring brake chamber to a low pressure region, and an immobilise position in which the spring brake control assembly is operable to connect the spring brake chamber to a low pressure region but cannot be operated to cause the flow of pressurised fluid into the spring brake chamber.