Why does Count Dracula going to England for?

I suppose the bluntest way of putting it is that Dracula is looking for new, young, fresh blood, because he has been predating on his own surroundings for centuries. As the Count says to Jonathan Harker:

"I long to go through the crowded streets of your mighty London, to be in the midst of the whirl and rush of humanity, to share its life, its change, its death, and all that makes it what it is........."