A power transmitter for wirelessly providing power to a power receiver via an inductive power transfer signal; the power transmitter comprising: a transmitter coil arranged to generate the power transfer signal; a driver arranged to generate a drive signal for the transmitter coil to generate the power transfer signal, the driver being arranged to generate the drive signal to employ power transfer time intervals during which the power transfer signal is arranged to transfer power to the power receiver; a receiver arranged to receive messages from the power receiver; a first controller arranged to control a parameter of the drive signal in accordance with a first mode of operation, the first mode of operation comprising operating a power control loop to control a power property of the power transfer signal in response to power control error messages received from the power receiver, a maximum duration between power control error messages being no more than 300 msec; a second controller arranged to control the parameter of the drive signal in accordance with a second mode of operation, the second mode of operation comprising setting the parameter of the drive signal in response to at least one power transfer signal setpoint received from the power receiver, the power transfer signal setpoint being indicative of a target power property for the power transfer signal, a maximum duration between power transfer signal setpoints being no less than a second; and a circuit arranged to select between the first mode of operation and the second mode of operation in response to a power transfer control mode request received from the power receiver; charcterized in that the driver is further arranged to generate the drive signal to employ communication time intervals during which a power of the power transfer signal is reduced relative to the power transfer time interval; the receiver is arranged to receive messages from the power receiver during communication time intervals; the second mode of operation comprises not operating any power control loop controlling the drive signal in response to power control error messages received from the power receiver; and in that the power transmitter further comprises a timing circuit arranged to vary a timing parameter for the communication time intervals dependent on whether the power transmitter is operating in the first mode of operation or in the second mode of operation, the timing parameter being a parameter selected from the group consisting of: a duration of the communication time intervals, and a frequency of the communication time intervals. a transmitter coil arranged to generate the power transfer signal; a driver arranged to generate a drive signal for the transmitter coil to generate the power transfer signal, the driver being arranged to generate the drive signal to employ power transfer time intervals during which the power transfer signal is arranged to transfer power to the power receiver; a receiver arranged to receive messages from the power receiver; a first controller arranged to control a parameter of the drive signal in accordance with a first mode of operation, the first mode of operation comprising operating a power control loop to control a power property of the power transfer signal in response to power control error messages received from the power receiver, a maximum duration between power control error messages being no more than 300 msec; a second controller arranged to control the parameter of the drive signal in accordance with a second mode of operation, the second mode of operation comprising setting the parameter of the drive signal in response to at least one power transfer signal setpoint received from the power receiver, the power transfer signal setpoint being indicative of a target power property for the power transfer signal, a maximum duration between power transfer signal setpoints being no less than a second; and a circuit arranged to select between the first mode of operation and the second mode of operation in response to a power transfer control mode request received from the power receiver; the driver is further arranged to generate the drive signal to employ communication time intervals during which a power of the power transfer signal is reduced relative to the power transfer time interval; the receiver is arranged to receive messages from the power receiver during communication time intervals; the second mode of operation comprises not operating any power control loop controlling the drive signal in response to power control error messages received from the power receiver; and in that the power transmitter further comprises a timing circuit arranged to vary a timing parameter for the communication time intervals dependent on whether the power transmitter is operating in the first mode of operation or in the second mode of operation, the timing parameter being a parameter selected from the group consisting of: a duration of the communication time intervals, and a frequency of the communication time intervals. a duration of the communication time intervals, and a frequency of the communication time intervals.