I'm sat doubting my own intelligence here....
Cooking food in the oven (for example fish fingers), we always put the food onto tin foil on a baking tray. Is this not normal? A friend just saw me doing it with oven chips and looked at me like I was nuts? I occasionally would use baking paper depending on what we have in the drawer....
Our oven is currently playing up and not heating food in the middle, friend suggested the fault was because I use tin foil.