Once a cheap staple for school lunch boxes and pub snacks, the humble crisp has been transformed into a hand-baked, organically oiled gourmet experience. From caviar to cheese and port, there's no flavour left unturned in the hunt for ever posher nibbles. But even in an era when crisps cost a packet, the news that the UK's most upmarket grocery store, Fortnum & Mason, is selling a tub of plain ones for £24.99 sounds eye-watering, rather than mouth-watering. So how much crunch do you really get for your upper-crust crisps? TANITH CAREY takes a bite... From caviar to cheese and port, there's no flavour left unturned in the hunt for ever posher nibbles