Might be a UK thing. Here in the US I don’t think I’ve ever been to a theater that allowed any outside food or drink. I doubt it’s because of safety, I’m pretty sure it’s because it would cut into their profits from concession stand sales.

To be fair, a lot of movie theaters ban bringing in outside food. At least in my experience. I agree with just not eating though. It would certainly be healthier to decouple moviegoing from snacking.