My Shiela Mary Mason fuschia has orange dust under its leaves?

Sounds like a rust infection - spray with a suitable fungicide.

Would agree, but it is odd, my book says that Fuchsia rust is rare in Britain, yet I have seen more questions about this year than ever before.

You're right about that Owdboggy - I've seen 3 questions on this in a week in various places, and I've never heard of it as a problem on Fuchsias before. Funnily enough, it was the same variety each time, so perhaps its particularly prone.