A transmission assembly for a power tool comprises a first transmission path comprising a high speed transmission path and a second transmission path comprising a low speed transmission path. Driven gears of each transmission path are permanently driven during operation of the transmission. A controller is provided for engaging or disengaging the high speed transmission path in response to monitored operating current of an electric motor providing a driving torque to an input of the transmission. When disengaged, a driven gear of the high speed transmission path continues to be driven, but the driven gear is disengaged from an output of the transmission. Consequently, under these circumstances, the low speed transmission path is the ‘active’ transmission path providing a low speed, high torque drive to the transmission output. A clutch enables the low speed transmission path to operate at a lower speed than an output of the transmission assembly when the high speed transmission path is engaged and is providing a high speed, low torque drive to the transmission output.