Vauxhall Zafira B - Exhaust emissions warning light - kayaker steve

I bought an 08 plate Zafira (1.6 petrol) in November 2011. A couple of weeks ago (during the very cold weather), and after having driven about 2,000 miles, the exhaust emissions warning light came on. I returned it to the dealer who cancelled the light and couldn't then get the fault to reappear. They returned it to me, basically to see what happens. Yesterday morning, after a cold (but no where near as cold as before) night, the light came on again. What will cause the light to come on? The car runs OK, but could any hidden damage have been caused (as I have driven some distance with the light on)? Is it reasonable to expect the dealer to rectify the problem at his cost (as I've not had the car 6 months yet)?

Vauxhall Zafira B - Exhaust emissions warning light - kayaker steve

Update - Took car back to the dealer who said that catalytic convertor had broken up and they fitted a new one, at no charge to myself. I'm still a little concerned as to why the cat on quite a relatively new car should break up? Was it a problem just with the cat, or could there be an underlying issue, which will cause the new cat to fail in the future (and probably at my expense then!). Anyone have any thoughts?

Vauxhall Zafira B - Exhaust emissions warning light - unthrottled

A failing coil pack is the most common cause of cat failure because it allows petrol AND air to enter the exhaust stream and the cat overheats.

People replace the coil pack(s) because the misfiring makes the car all but undriveable, but they don't bother to replace the cat if they can just reset the emissions light and sell the car!

I wouldn't be too concerned. If the car passed its MOT and runssmoothly, it is probably fine!