Abstract: Variable ratio steering mechanism comprising a body in which is rotatably mounted an input shaft, a drive shaft having a longitudinal axis, and coupled to the input shaft so as to be rotatable therewith, an output member slidably mounted in the body, a screw mechanism connecting the drive shaft and the output member so that rotation of the drive shaft produces a corresponding displacement of the output member in the body, characterized in that the drive shaft is axially slidable with respect to the input shaft, the steering mechanism further comprising a displacement mechanism to selectively displace the drive shaft axially with respect to the input shaft, the displacement mechanism comprising a screw connection between the drive member mounted in the body.