Update;
Ok, so checked for continuity on the sensor wires using my multi-meter set on the ohms range, moving the car back and fore I got a very high reading every time the magnets passed the reed switch, however; the reading was in the meg ohm, and I presume should be nearer dead short as the switch closes, so some good news in that the magnets on the wheel seem to be fine, its obviously an issue with the reed switch itself, or the wires going to it, so next step when I get a bit more time, I will be examining the rest of the wiring going to the sensor, and if all found to be intact, then unfortunately it looks like the sensor will need to be removed/exchanged!
Ant.
PS, any picks of where to find the sensor on the gearbox would be great!