So yesterday morning, I woke up to random piles of cat sick everywhere, and a very miserable looking kitty. I hadn't given her any different food, and she doesn't go outside, can't have eaten anything nasty from outside. I couldn't work out what the heck she could have eaten to make her so poorly!
Then I saw that her food bowl had been moved. DH had moved her food bowl while he was cleaning the kitchen floor, and put it right under the radiator!! I had a poke around in her wet food, and it appears that the heat from the radiator had kind of "cooked" her food that she's left from the night before....it smelled absolutely rancid! I've come to the conclusion that she must have eaten what she wanted that night when it was fresh, and then gone back for another nibble later on after the hearing had been on for a while 
She appears to be ok today, and is eating fresh food and drinking plenty - that's away from the radiator!
Cannot believe that amount of stupid came from my DH 