My sister has a four year old Fabia and the imisions warninglight has come on. She took it to a garage who checked the emsions levels and said they are all right. I have told her to take it to a Skoda garage who will connect it up to a computer but does anyone have any knowledge of this problem?

There has been a fault detected within the engine management system that could potentially affect the emissions. Getting the codes read will be a start to fixing the problem. As you do not state which engine the car has, I cannot suggest which sensor may be playing up.