A braking system for a vehicle comprising: a cam coupled to a transmission shaft or a trailing wheel for rotation therewith, the cam comprising a circumferential cam face; at least two hydraulic cylinder assemblies (126, 129), each assembly (126, 129) comprising a cylinder and a piston (125, 130) configured to reciprocate relative to one another and a cam follower attached to either the cylinder or the piston (125, 130) and arranged to contact the cam face, whereby rotation of the cam causes the cam follower and the cylinder or the piston (125, 130) to which it is attached to reciprocate relative to the other of the piston (125, 130) or the cylinder; a hydraulic circuit connecting the hydraulic cylinder assemblies (126, 129) together through which hydraulic fluid flows as the cylinder and piston (125, 130) of each assembly (126, 129) reciprocate relative to each other; a master brake valve configured to control the flow of fluid around the hydraulic circuit; and an actuation system comprising a user input device configured to actuate the master brake valve; wherein actuation of the master brake valve obstructs the flow of the fluid in the hydraulic circuit, such that the relative reciprocation of the cylinder and the piston (125, 130) of each assembly (126, 129), and reciprocation of each cam follower, is inhibited or prevented whereby the cam followers thereby inhibit or prevent rotation of the cam; and being characterized in that the cam face comprises first and second flat faces (142, 143) configured such that, as the cam rotates, each cam follower comes into contact with a respective flat face (142, 143) at the same time; wherein the cam rotates about an axis of rotation and each hydraulic cylinder assembly (126, 129) is located along a reciprocating axis which intersects the axis of rotation of the cam and the first and second flat faces (142, 143) are located at diametrically opposed locations on the cam; and wherein the cam is symmetrical about an axis of symmetry which intersects the axis of rotation, such that a perigee of the cam and an apogee of the cam are opposite to one another, and the first and second flat faces (142, 143) are located at the apogee and the perigee of the cam. a cam coupled to a transmission shaft or a trailing wheel for rotation therewith, the cam comprising a circumferential cam face; at least two hydraulic cylinder assemblies (126, 129), each assembly (126, 129) comprising a cylinder and a piston (125, 130) configured to reciprocate relative to one another and a cam follower attached to either the cylinder or the piston (125, 130) and arranged to contact the cam face, whereby rotation of the cam causes the cam follower and the cylinder or the piston (125, 130) to which it is attached to reciprocate relative to the other of the piston (125, 130) or the cylinder; a hydraulic circuit connecting the hydraulic cylinder assemblies (126, 129) together through which hydraulic fluid flows as the cylinder and piston (125, 130) of each assembly (126, 129) reciprocate relative to each other; a master brake valve configured to control the flow of fluid around the hydraulic circuit; and an actuation system comprising a user input device configured to actuate the master brake valve; wherein actuation of the master brake valve obstructs the flow of the fluid in the hydraulic circuit, such that the relative reciprocation of the cylinder and the piston (125, 130) of each assembly (126, 129), and reciprocation of each cam follower, is inhibited or prevented whereby the cam followers thereby inhibit or prevent rotation of the cam; and being characterized in that the cam face comprises first and second flat faces (142, 143) configured such that, as the cam rotates, each cam follower comes into contact with a respective flat face (142, 143) at the same time; wherein the cam rotates about an axis of rotation and each hydraulic cylinder assembly (126, 129) is located along a reciprocating axis which intersects the axis of rotation of the cam and the first and second flat faces (142, 143) are located at diametrically opposed locations on the cam; and wherein the cam is symmetrical about an axis of symmetry which intersects the axis of rotation, such that a perigee of the cam and an apogee of the cam are opposite to one another, and the first and second flat faces (142, 143) are located at the apogee and the perigee of the cam.