A steering column assembly comprising an inner tube and an outer tube that surrounds the inner tube along at least part of its length, in a relaxed condition the outer tube being a relatively loose fit around the inner tube, an elongate slot in the outer tube which can be at least partially closed by applying a load either side of the slot to cause a reduction in the internal diameter of the tube, the slot extending along the outer tube starting from one end of the tube, a pair of flanges which are fixed to the tube on opposing sides of the slot, and a clamp mechanism which connects one flange to the other, the clamp mechanism being movable between a clamped position in which it applies a clamping force to the flanges that acts to reduce the width of the slot and so tightens the outer tube around the inner tube, and an unclamped position in which the clamping force is reduced to permit the flanges to move away from one another as the tube returns towards its relaxed condition. A restraining member that extend around the whole outside of the circumference, or substantially around the whole circumference, of a length of the outer tube that is located at, or close to, the end of the outer tube at which the slot starts, the restraining member preventing unwanted deformation of the end of the outer tube.