Phew!

I got a reply from Heinz very quickly asking me to give them a ring so I did. The Customer Services lady I spoke to just now said that very few Heinz products have palm oil in them and the vegetable oil they use in salad cream is rape seed oil or sunflower oil. I should've asked why they don't know which one but perhaps they standardise their labelling. Either way, I don't really mind which it is so I'm just leaving it at that - one of life's little mysteries!