why have i got a white covering on the leaves of my lupin

Not sure Gayle but one of my Geraniums does too.
It's got to be an aphid/pest of some type, i sprayed with an insecticide 2 days ago but i've not noticed any difference yet.

Sounds like mildew which is a fungus. Spray with a suitable fungicide. Take care, Louise, Geraniums are a bit odd with some sprays, they tend to die, so read the instructions.

a long shot is it the dried slime of a slug/snail?

I have seen this many times before it is mildew,owdboggy is right soray with fungiside and make sure they are well watered as mildew thrives in dry conditions.

We've both learnt a lot there Gayle.
Thanks for the advice there Owdboggy.