A collapsible steering column assembly comprising a steering shaft that is supported within a steering column shroud, the shroud comprising an upper shroud portion and a lower shroud portion, in which the upper shroud portion is located towards the end of the steering shaft that is nearest the steering wheel and the lower portion is located towards the end of the shaft furthest from the steering wheel, the upper portion being at least partially received within the lower portion so that the upper portion can telescopically collapse into the lower portion during a crash, a support bracket that in use is secured to a fixed part of the vehicle and includes two support bracket arms that depend from a base portion to embrace the shroud, a clamp rail that is releasably secured to the upper shroud portion, the clamp rail including a slot that extends generally horizontally, and a clamp pin that extends through an opening in each of the arms of the bracket and through the generally horizontal slot in the rail, the clamp pin carrying a clamp mechanism that is movable between an unclamped position in which the rail can move freely relative to the clamp pin and a clamped position in which the rail is fixed relative to the clamp pin. The rail is secured to the upper shroud portion by a deformable tab which protrudes from the upper shroud portion to hook onto a part of the rail that faces the steering wheel end of the shroud. In use of the assembly with the cam mechanism in the clamped condition the tab is deformable under a predefined load applied to the upper shroud so as to unhook from the rail allowing the upper shroud to move axially relative to the rail and hence relative to the clam pin to permit collapse of the steering column shroud.