What you are describing are iron filings / contaminants. All cars have them, even new, but they are more noticeable on white cars. If cars have been stood near railway lines for example or stood in compounds for a while, this is how they can be picked up, along with general air contaminants. You can buy products to get rid of these, Ironx - see link below however as you have supaguard on your car I'm not sure how it will work. There's a good chance it will reduce it the supaguard protection.
http://www.cleanyourcar.co.uk/engine-an ... d_726.html
I use Ironx on my car, every time I do a full detail, which is about twice a year. Claying takes the top off, as you have discovered by taking the top off with your finger nails, unfortunately the rest is still imbedded in the paintwork, hence the need for Ironx. Don't be alarmed by Ironx when you come to use. After you have washed the car in the normal manner and dried it, you spray the Iron x onto a panel and leave for 2 - 5 minutes. All the iron particles on the car start to turn bright red and depending on how bad the car is, looks like its bleeding. As I said, don't be alarmed, just rub the panel with a microfibre cloth to get rid of the red marks and then rinse and dry, then onto the next panel, working around the car. There's was hardyly any on my car when I gave it its winter detail a few weeks ago, when using the Ironx. If you keep on top of it, they will be vastly reduced in months to come.
Thanks RCZ1, but I thought having the paintwork protected would have stopped this? I had another look this morning and it is getting worse.When it goes in to morrow to get the rattling dashboard sorted I will mention it and see if they can do something for me...
https://lh5.googleusercontent.com/_8CEF ... rge%29.JPG