A cleaner head includes a drive mechanism connecting a drive means to a rotatable brush member. The drive mechanism comprises an input drive member connected to the drive means, an output drive member connected to the rotatable brush member, and a flexible drive element extending therebetween. The drive mechanism is provided with an adjustment mechanism operable to vary the distance between the input and output drive members in order to vary the tension of the flexible drive element. The adjustment mechanism is movable in a first direction from a first position in which the flexible drive element has a relatively low tension through a plurality of further positions which increases the tension in the flexible drive element. The adjustment mechanism is lockable in a selected one of the plurality of further positions against movement in a direction opposite to the first direction.