Ah yes, someone from Bournemouth!
How long have you had it for? anodised aluminium is not meant to get corroded after a very long time. Maybe desmutting might work.
I used 70% isopropyl alcohol (aka rubbing alcohol) and a rag last night on the aluminum casing. Works great!
Usually just use 70% EtOH from my lab. Works equally well.
isopropy alchol might ruin metal case. Call Apple ask how to clean it for your own safe than big time sorry
I used chlorox wipes once. It seemed to work great. I used them because I had let a friend use my laptop for a while, and I don't really like sharing keyboards.