My passenger seat adjusted correctly except the forward and back motion. I was expecting to have to get the motor out and give it a good bashing and oiling. Fortunately, the forward-back motor is actually bolted to the seat rails rather than on the seat. As the controls are fitted to the seat there is a loom that runs from the seat to the rail-motor. This can be disconnected using an in-line connector which is found under the seat.

I was very happy to find that the connector had become dislodged and separated. I would guess that the cause of this is leaving something heavy behind the seat that has shot forward under braking. I simply adjusted the seat to the highest setting and reconnected the connector pair:

I was so chuffed when the seat worked again I didn't have a cup of tea.......