A locking device is disclosed for preventing rotation of one component relative to another component to which it is connected. The locking device comprises a locking plate having a component engaging portion to engage one component, A surface of the locking plate is grooved to engage with a grooved surface carried by the other component. One or more fixing holes are provided for one or more fixing members to be passed through, to force the grooved surface of the locking plate into engagement with the grooved surface carried by the other component.