Anything sold in the UK and EU as 'honey' should be 100% honey, where honey is entirely derived from bee collected nectar.
BUT I believe that some producers leave out sugar water to help 'feed' the bees. This is fine when there's no nectar around as it stops the bees starving, but when there is nectar available the bees gather it and store it in the hive, diluting the real honey. It increases the yield from a piece of land as you can keep more bees than would otherwise be possible, but it dilutes the real honey with flavourless sugar.
As a result cheap honey doesn't taste of much at all. These days £4.20+ for a 340g jar seems to be the price to get something with actual honey flavour.