An electric power assisted steering system comprising: a torque sensor assembly comprising an input shaft that in use is operatively connected to a steering wheel of the vehicle, an output shaft that in use is operatively connected to the road wheels of the vehicle, a torsion bar that interconnects the input shaft and the output shaft, and a processing means which produces a torque signal indicative of the torque carried by the torsion bar, an electric motor that is connected to the output shaft so that a change in the angular position of the motor produces a corresponding change in the angular position of the output shaft, and a motor position sensor that provides a motor position signal dependent on the angular position of the motor rotor that repeats each time the motor has rotated through a known angular range such as once per motor rotor electrical rotation, the apparatus further including processing means that generates an absolute output shaft position signal from the motor position signal by adding to the output of the motor position sensor a first term indicative of the fixed offset between the motor position sensor zero position and the zero position of the input shaft and a second term indicative of the number of turns of the motor rotor away from the zero position of the input shaft, characterised in that, the processing means is adapted to determine the base motor position value at start up of the system by comparing the motor position signal from the position sensor with the signal from the sensor associated with the sensing means of the upper shaft to determine a central, most likely, candidate, choosing a higher candidate that is one repeat of the motor sensor signal above this and a lower candidate that is one motor position value below this, and during subsequent unpowered motion of the steering system producing a torsion bar deflection value from each candidate by comparing the absolute lower shaft signal with the signal from the upper shaft sensing means and ruling out the candidates that give implausible torsion bar deflection values over time as the steering system moves until only one remains plausible candidate. a torque sensor assembly comprising an input shaft that in use is operatively connected to a steering wheel of the vehicle, an output shaft that in use is operatively connected to the road wheels of the vehicle, a torsion bar that interconnects the input shaft and the output shaft, and a processing means which produces a torque signal indicative of the torque carried by the torsion bar, an electric motor that is connected to the output shaft so that a change in the angular position of the motor produces a corresponding change in the angular position of the output shaft, and a motor position sensor that provides a motor position signal dependent on the angular position of the motor rotor that repeats each time the motor has rotated through a known angular range such as once per motor rotor electrical rotation, the apparatus further including processing means that generates an absolute output shaft position signal from the motor position signal by adding to the output of the motor position sensor a first term indicative of the fixed offset between the motor position sensor zero position and the zero position of the input shaft and a second term indicative of the number of turns of the motor rotor away from the zero position of the input shaft, characterised in that, the processing means is adapted to determine the base motor position value at start up of the system by comparing the motor position signal from the position sensor with the signal from the sensor associated with the sensing means of the upper shaft to determine a central, most likely, candidate, choosing a higher candidate that is one repeat of the motor sensor signal above this and a lower candidate that is one motor position value below this, and during subsequent unpowered motion of the steering system producing a torsion bar deflection value from each candidate by comparing the absolute lower shaft signal with the signal from the upper shaft sensing means and ruling out the candidates that give implausible torsion bar deflection values over time as the steering system moves until only one remains plausible candidate.