A lock cylinder comprising: a housing including a wall defining a hollow portion, and a pin portion defining at least two outer pin chambers; outer pins disposed in each of the outer pin chambers; a plug including a body rotatably housed within the hollow portion of the housing, the housing and the plug cooperating to define a shear line, the plug defining a key slot extending at least partially through the body in a longitudinal direction of the plug, the plug further defining at least two inner pin chambers disposed within the body and in communication with the key slot and selectively aligned with the outer pin chambers, and an auxiliary pin chamber in communication with the key slot; inner pins disposed in each of the inner pin chambers and extending partially into the key slot such that the inner pins are engageable by a key; and an auxiliary pin disposed in the auxiliary pin chamber and in communication with the key slot, the auxiliary pin including a first projection defining a first engagement surface engageable by a key to move the auxiliary pin to a withdrawn position to allow rotation of the plug relative to the housing, and a second projection spaced apart from the first projection and defining a second engagement surface generally facing the first engagement surface and engageable by the key to move the auxiliary pin characterised in that the second engagement surface is engageable by the key to move the auxiliary pin to a projecting position in which the auxiliary pin projects from the plug and is engageable with the housing to prevent rotation of the plug relative to the housing; and wherein the auxiliary pin includes a substantially cylindrical upper portion and a lower planar portion. a housing including a wall defining a hollow portion, and a pin portion defining at least two outer pin chambers; outer pins disposed in each of the outer pin chambers; a plug including a body rotatably housed within the hollow portion of the housing, the housing and the plug cooperating to define a shear line, the plug defining a key slot extending at least partially through the body in a longitudinal direction of the plug, the plug further defining at least two inner pin chambers disposed within the body and in communication with the key slot and selectively aligned with the outer pin chambers, and an auxiliary pin chamber in communication with the key slot; inner pins disposed in each of the inner pin chambers and extending partially into the key slot such that the inner pins are engageable by a key; and an auxiliary pin disposed in the auxiliary pin chamber and in communication with the key slot, the auxiliary pin including a first projection defining a first engagement surface engageable by a key to move the auxiliary pin to a withdrawn position to allow rotation of the plug relative to the housing, and a second projection spaced apart from the first projection and defining a second engagement surface generally facing the first engagement surface and engageable by the key to move the auxiliary pin characterised in that the second engagement surface is engageable by the key to move the auxiliary pin to a projecting position in which the auxiliary pin projects from the plug and is engageable with the housing to prevent rotation of the plug relative to the housing; and wherein the auxiliary pin includes a substantially cylindrical upper portion and a lower planar portion.