The driver seat does have the sensor, always red when I sit in it, goes green when I belt up, this is the same for the 2 rear seats. The front passenger seat is always green even if the belt is not done up.
I'll ring mangoletsi see what they say but I personally think the passenger seat sensor should behave the same way as the others.
Cheers
You've misunderstood what I wrote - I'm not talking about sensors to determine if the belts are done up or not - all the belts have those.
What I'm saying is that the front passenger seat also has a sensor to determine if a passenger is present or not, which none of the other seats have.
If the front passenger seat is occupied it should show red under the same conditions as the others (not sure if has a delay in detection, mind you) - have you tried having a passenger (or even yourself) sit in the front passenger seat?

If you have a passenger sit in the passenger seat and set off then go over 20kmh or over 10kmh for more than 5 seconds you should hear an audible warning.
The manual isn't terribly clear about this passenger seat behaviour:
Passenger
A similar situation arises for the front passenger, except that the
warning lights becomes green and the signal also stops when the
passenger leaves the car. In the event that both front seat belts are
unfastened with the vehicle in motion, a few seconds apart, the
acoustic signal refers to the most recent event, while both warning
lights display a visual signal independently of one another.
"The warning light becomes green and the signal also stops when the passenger leaves the car" - slightly mangled way of it saying the light is green if there's no front passenger, I believe.