From Halfords you can get Gunk, it's OK, but a bit overpriced IMO. You can get "real" engine degreasers from smaller auto-parts store. Say you're going take an old engine apart or something and they'll give you the good stuff.
Just washed my bike on Friday evening and the whole area came up squeaky clean. Just used about 20mm in the bottom of a small glass jar and a brush to apply it, on the rim, the sprocket, chain, swing arm, centre stand, etc. Washed it off with water.
Then I used the Castrol Greentech (expensive, but pretty good) to wash the area again. Usually spray a bit on the area directly or onto a £1 IKEA dish brush.