I've got a stone coloured London Fog which can start to look grimey from being worn on public transport etc, its a poly/cotton mix as I think they all are. I just bung it in the machine on a cool wash and let it dry naturally, the same with the liner. I've washed the mac 2 or 3 times without any issues. It still seems 'rain resistant' although I've never worn it in a sustained downpour. I guess you could consider Nikwax or some other waterproofing product, as long as it doesn't leave a residue on dark colour cloth.

My London Fogs have maintained their resilinacy after machine-washing, as they're designed for that.  But I have used that 3M Scotchguard waterproofing spray with 60/40s and Baracutas succesfully in the past.

^^^ Gave it a good clean, and a re-spray with Nikwax and it's good to go. At £30, it looks brand new. Why anyone would pay £100s for a new inferior version of these raincoats I can't understand. Thanks, All.