Before I moved up here I went to my old stomping ground at Thursley with some friends specifically so I could see some of the species that havent reached the Highlands yet (give it a couple of decades though and Climate Change will see us right!) and we saw plenty of hobbies, tree pipits, redstarts and stonechats but no dartford warblers. No one we saw that day (including a group of birders) had seen any.