Thanks gents, yes I can imagine that a generic MOT centre might have trouble interpreting this indicator and could fail the car, hopefully a Ford centre would have more nouse.
There is indeed an airbag warning light in the instrument cluster that briefly lights during ignition and then extinguishes when the car is running so I would hope that a tester would be looking out for that.
From looking on autotrader I have seen many Ford S-Max (2015-) models showing this indicator lit on their interior photos, so looks to be a standard “feature” on this particular model. Fortunately it’s outside the drivers field of vision else it would be incredibly annoying!
