Its mostly been said but I just thought I'd add some of my experiences.
I worked as a "dinnerlady" at my children's school for just under a year.
Whilst the school has an "healthy eating" status, they don't seem quite as stringent as some, which makes me wonder if the schools who state healthy eating are knee jerking a little, unless perhaps it differs from area to area, which is plain stupid.
Dinnerladies or Midday Assistants are generally only food police in that it is part of their role to filter down the guidelines or restrictions by way of supervision. No idea how it works in a high school but in our small-ish primary, they walk up and down breaking up arguments, opening fucking frubes, and generally making sure that at least half a sandwich is eaten before the fucking frube gets eaten, and in hot dinner case that only 2 items of a main course are left on the plate before moving on to pudding.
The puddings are pretty pudding-ish, however our school doesn't ban home made cake, flapjacks, cereal bars, or biscuits, but does "ban" chocolate bars (so a penguin is okay yet a couple of squares of Green & Blacks isn't), which is silly in my book. Sweets and fizzy is banned, but generally its not crazy like no white bread ham cheese etc, that would be considered OTT.
There are some inconsistencies regarding Dinnerladies interpreting what they consider to be "healthy eating" policies - some of them are not nutritional experts nor are they terribly academic, others are. I observed a colleague giving my own son a healthy eating sticker one day when he had a sizeable slab of Hello Kitty birthday cake of my daughters of which I was attempting to get rid, yet the child opposite him didn't get one on the basis that he had a penguin. Silly really, as the sugar in the icing alone would top that of the penguin. It wasn't even homemade cake. I would have picked her up on it and it wasn't because it was my own son that I didn't, simply I was not her boss and she had enough issues with me anyway I let it slide and just made a mental note to try and even up the score with the stupid chuffing stickers at some point in the future to poor penguin-boy.
Apparently our school no longer do apple and orange juice for hot dinner people at lunchtime due to the government (don't know if its interpretation or blanket rule) yet a packed lunch can have a carton of juice. You can't, however, send your child in with a bottle of sugar free squash to drink outside of lunchtimes on a hot day for instance.
Because we can send in cake and custard etc it doesn't seem too much of a difference between hot dinners and packed lunches, but if they were to remove this category of foods from packed lunches things would be very different indeed and that's where the healthy eating policy can seem very hypocritical indeed.