A brake actuator (10) having a housing (12) in which is provided a movable brake actuating assembly (18, 30), the brake actuating assembly (18, 30) being movable between a brake apply position which, in use results in the application of a brake to which the actuator (10) connected, and a brake release position which, in use, results in the release of the brake, the brake actuator (10) further including a lock (34) which is operable to prevent movement of the brake actuating assembly (18, 30) from the brake apply position to the brake release position, the brake actuating assembly (18, 30) including a first movable member (18), a second movable member (30) and a resilient biasing element (32) which extends between the second movable member (30) and the first movable member (18) and which, if one of the first or second movable members (18, 30) is moved relative to the other from an equilibrium separation, exerts a force tending to return the first (18) and second (30) movable members to the equilibrium separation, the brake actuator (10) further including compliance control chamber (50) between the first movable member (18) and the second movable member (30), the compliance control chamber (50) having a port (58a) and being sealed such that flow of fluid into or out of the compliance control chamber (50) other than through the port is substantially prevented.