Best £4 i've ever spent on a cleaning product - and i bought it for my exhaust, not the wheels.
AutoSol Metal Polish
A Before shot: (Old photo, wheel was even worse when i cleaned it yesterday)

I know its not 100% immaculate, but a hell of a lot better than it was. I am going to take the two front wheels off when i get a nice day i'm free and try get the bits in the corners sorted.
After Picture: (It started to rain)
