A power tool, typically battery-operated, such as a lawnmower, comprising: a driven element (9), an electric motor (7) coupled to the driven element so as to drive the driven element, an electric power source (2) electrically coupled to the motor (7) so as to supply electric current to the motor (7) and a control circuit (3) arranged to control the supply of electric current to the motor (7) from the power source (2), and a current sensor (6) operable to output a current signal indicative of the current flowing through the motor (7) in which the control circuit (3) has a high speed mode (40) and a low speed mode (32), the control circuit (3) being arranged so that: when it is in the high speed mode (40), the control circuit supplies electric current to the motor (7) so as to attempt to drive the driven element (9) at a first desired speed (54) when it is in the low speed mode (32), the control circuit supplies electric current to the motor (7) so as to attempt to drive the driven element (9) at a second desired speed (52) which is lower than the first desired speed (54) and the control circuit (3) switches between the high speed mode (40) and the low speed mode (32) dependent on the current signal. As such, energy can be saved by efficient use of electrical power, by increasing the speed of the driven element when the load increases.
