Left for work, car running fine, called in to get petrol one mile into journey. Fuel gauge was just below quarter of a tank and I added another thirty pounds worth. Started car back up and it immediately felt lumpy. Idled ok'ish but when I pulled away it was definately misfiring. After about one hundred yards it cleared itself and ran ok for a further four miles.

Then the misfire came back with a vengeance and I struggled to get it back home. It had no power and was juddering like a barsteward. The EML (picture of engine) was flashing for a few seconds and then stayed on permanently. I limped it home and had a quick look under the bonnet. Nothing amiss that I could see so I started it back up again. No warning lights stayed on and it revved up like a good-un, no misfire at all. Have to give it a blast in the morning to see if it plays up again. Surely contaminated fuel wouldn't have affected it that quick as it wouldn't have even got through the pipes when it happened.
Anyway, because I'm at work now, I got SWMBO to read the codes via pedal trick and this is what she got. (yes she did check them several times before confirming)

P0430 Catalyst System Efficiency Below Threshold (Bank 2)
P0300 Random/multiple cylinder misfire detected
P0304 Cylinder 4 Misfire Detected
Car is 52 plate 3.2
I've never had the eml come on before, even with the known lambda issues on other peoples cars.

Any ideas?
Regards
Alan