A clamp mechanism for a steering column assembly comprising: a support bracket; a clamp pin that passes through an elongate slot in the support bracket and an opening in a shroud of the steering column; a fixing member; a toothed rack carried by the support bracket in a position facing the fixing member, the toothed rack comprising a plurality of recesses each spaced from an adjacent recess by a land, the toothed rack extending alongside the elongate slot; a locking pin located in a bore in the fixing member that is biased in a direction towards the toothed rack by a spring; and clamp means that in use causes the fixing member to move between a clamped condition and unclamped condition; in which in the clamped condition the locking pin engages with the toothed rack such that the pin is either located in one of the recesses and thereby prevents movement of the clamp pin along the elongate slot in at least one direction or engages a land under sufficient force from the spring that any subsequent movement of the clamp pin along the slot whilst in the clamped condition will cause the pin to move into a recess, and in which in the unclamped position of the fixing member the locking pin is either held clear of the fixed rack or contacts the fixed rack with insufficient force from the spring to retain the lock pin within a recess of the fixed rack, thereby permitting free movement of the clamp pin along the slot, wherein the clamp means includes a cam mechanism having a fixed cam member and a moving cam member (16, 17), and characterised in that the fixing member comprises one of the fixed cam member and the moving cam member. a support bracket; a clamp pin that passes through an elongate slot in the support bracket and an opening in a shroud of the steering column; a fixing member; a toothed rack carried by the support bracket in a position facing the fixing member, the toothed rack comprising a plurality of recesses each spaced from an adjacent recess by a land, the toothed rack extending alongside the elongate slot; a locking pin located in a bore in the fixing member that is biased in a direction towards the toothed rack by a spring; and clamp means that in use causes the fixing member to move between a clamped condition and unclamped condition; in which in the clamped condition the locking pin engages with the toothed rack such that the pin is either located in one of the recesses and thereby prevents movement of the clamp pin along the elongate slot in at least one direction or engages a land under sufficient force from the spring that any subsequent movement of the clamp pin along the slot whilst in the clamped condition will cause the pin to move into a recess, and in which in the unclamped position of the fixing member the locking pin is either held clear of the fixed rack or contacts the fixed rack with insufficient force from the spring to retain the lock pin within a recess of the fixed rack, thereby permitting free movement of the clamp pin along the slot, wherein the clamp means includes a cam mechanism having a fixed cam member and a moving cam member (16, 17), and characterised in that the fixing member comprises one of the fixed cam member and the moving cam member.