Man, this brings me back to my childhood.
Laban-Up is a Middle East favourite. A sour buttermilk drink that's so refreshing when served chilled on a sweltering hot day. It has a very distinct and comforting flavour and a cute old fashioned carton that I miss seeing.
Costs roughly 10 pence, found in all good (and bad) grocery stores and supermarkets around here.
PS: For those who have tried 'salty' Indian Lassi, it's similar to that.