Tuesday 17 January 2012 8.40pm
I'd get someone like Paul http://www.miracledetail.co.uk
to have a look at it (he's not cheap, but does an excellent job)
You're never going to prevent the train deposits from damaging your car unless it's covered.
If your car genuinely has been waxed frequently then there's a good chance that the rust spots are iron deposits on the top of the paint and can be removed with a little [professional] effort.
Very few people take any notice of their paintwork in central London, so even though many others will be affected you're probably the only one that cares or notices!