I think this is where the confusion comes from. lick and stick haven't been generally available to regular buyers for some years now (i.e. go to a store that sells stamps and you get a book of 6 or 12) and the available ones are generally self adhesive. Great fun when my toddler finds a fresh book of "stickers" to stick all over the house...
The situation is different with sheets of stamps that the post office has but most of the time they just print a generic postage label with the exact denomination required so it's rare to get issued as a punter a lick and stick. as a result any "unused" UK stamps on ebay are ones that have been successfully lifted from unfranked letters (yes it's possible, despite the tear-holes cut into them)