Asda are currently selling the 5 pack dairy milk multipack bars at £1.00. All types.
This doesn't work out very well with the normal dairy milk bars as you can buy a 9 pack for £1.58 or so. But the other varieties are normally sold at around £1.50 for a 5 pack.
So this works out pretty well if your looking for the other varieties.
Not sure whether online or not as i have only seen it instore.