Thanks everyone, I think I was just being a bit impatient. A couple of hours of airing the place after the cleaning did the trick. Has well and truly put me off supermarket own brand cat food though! I'll not be trying to economise on that again.
You need a odour neutraliser expecially for animal smells, you can get one from a pet shop they are very effective. Or wipe over with bio laundery liquid and leave for a while, the enzymes in it will breakdown the smell.
Fed the cat this morning and one of the sachets poured out as liquid, instead of expected jellied meat. I binned its contents and put bin bag outside, and immediately washed the cat bowl and food tray. I also sprayed odour neutraliser spray around and cleaned the floor under the tray. But the rank smell is lingering, despite windows being open. It's really really foul. Do we just have to wait till it dies down? Any brilliant suggestions?