Take delight in the fact that these increasingly rare visitors have honoured you with their presence!! I would be delighted to have their droppings on my house. Could you not scrub said droppings away at the end of the season? A ladder and a bucket of water should do it.
If you contact R.S.P.B. They will tell you whether or not you can legally destroy the nests.
Keep in your mind the fact that these tiny birds,weighing a matter of grams have flown thousands of exhausting miles,arrived here,built their nests(no mean feat in itself!) only to have someone poke it to pieces with a broom handle. Have pity,please!