Found this on a U.K. site. Not the Harrop Hairwing Dun; this one's Wulff/Quigley-like.

hook - Dai Riki 300 #10
thread - Danville 6/0 brown
tail - pheasant tail
rib - Uni-Stretch camel
body - dubbing march brown
hackle - badger
wing - grey squirrel dyed yellow (1Tbsp Rit Yellow in 1 cup water)

Part 1

mash barb, start thread at 2/3 mark

measure (hook length) some pheasant tail fibers; tie in/trim

clean, stack, measure (hook length) a clump of squirrel tail; tie in with tips facing over the hook eye, trim butts at an angle

tie in ribbing

dub thread/dub body to the 2/3 mark