Guys, thanks for all your advice (and, yes MMD, I have sinned!). I drove the car in London in the rain quite a lot today and the rust seems to be going away now. I will certainly try to avoid in future, as I don't really want to replace my order for nice new snow tyres for my ski trip to Austria next month with new rotors instead!
I have no hair dryer (or power) in my Garage to dry the wheels after washing so I think I will do this by just driving around for 10 mins or so to heat them up and dry them off that way. My main worry is with the vibration I now get at over 70 mph - was really heavy when I tried yesterday, but I presume that will go away too.
Thanks again - great forum.

SoS.
Atlas Grey 997 C2S
Cocao interior and all the usual gubbins.