I know, I know

Must sort out some LPG kits. They'll shaft us on that eventually, of course, but they've got less of a head start.
.. and Brown defines the word "snake" IMHO. he's looted everything in this country to prop up his famously "good economy", and how that's not his job any more we stand to suffer the consequences.
Anyway, when you say the light has been on do you mean the emissions light? (picture of engine). Mine has been on recently but before I got round to reading the codes it went out again. Came on after I drained the tank to vapours then filled up at a different garage to my normal one. Came on within 1/2 a mile of taking on fuel, and cleared after a week or so.
Having said that, I have seen trouble codes relating to the cat efficiency appear on my car without the light. I think they have to occur with a certain freqency to light the light but are stored regardless. At 60k miles I find it hard to believe there's a real problem and the emissions at MOT were down in the noise.
Mark posted some thoughts about this being due to the pre-cats (which is what are monitored) being a bit marginal on a 3.2 and thus they trip the warning every so often. Because emissions are taken after both cats, the second cat cleans up anything that the pre-cat doesn't, so MOT emissions are never an issue.
Apparently a dose of cataclean helps, so if you are thinking of passing the car on, that might be an idea, followed by a reset of the light. IME, sticking to one brand of fuel helps too. Maybe it allows the long term fuel trim to stabilise.
Kevin