Thanks that was great advice, I bought some Iron X from Auto-DNA, it works really fast and I tried it on the paint work as well, I could not believe how much brake dust just dissolved off ( it is scary to think all that is sitting on my bonnet, no wonder cars rust so easily)
I found this great site with so much how-to info. Have a look as they give very detailed info on cleaning and caring cor your rims and mags: http://www.incrediblydetailed.com/clean-wheels-and-tires/
Carl, try the CarPro Iron X, it works fast and very well. They also have a product called Iron X Paste that works really well for thick brake dust build-up and contaminants. When you have applied it, let it dwell for a while till all debris has loosened, you can also use a brush to agitate the surface for a better, faster result.