We lived in the headlice hotspot last summer (there's a map online showing which schools are currently affected) and mine kept getting reinfected, I know now because I just wasn't combing/treating effectively enough to prevent new hatchlings. The village chemist actually offers free lice treatment now, so it must have been bad.
Stickup on lotions where you can, they're currently £12-15 a pop for one bottle and you'll need 3 or 4 of them to treat a whole family. I've found that places like pound shops, Home Bargains and cheap chemists often stock them very cheaply.
Hedrin is mostly recommended as the last of the lotions they're immune to, but I pooled an amount in a dish to drop in the ones I'd combed out and by morning over half were still alive, so ...
My children have not had them since I started braiding her hair tightly and then spraying leave-in conditioner all over, working on the theory that the eggs can't stick to slippery hair shafts, which also mirrors the old wives tale that only clean hair gets lice, as greasy hair is too slippery.
My daughter had the lice at least 3 weeks before school put up posters in the windows and school gates. They cold do with printing off leaflets to put in all school book bags with advice on now to effectively treat them. They can't pull the old 'resources/costs' one on that because my daughter's bag is stuffed with pizza delivery another junk mail on a regular basis.