I get this quite often and it doesn't seem to harm the plant. Seems to happen mostly in autumn. But its a good idea to remove and destroy the affected leaves. I think Hywel once told me what it is but I don't remember.

It's most likely Fuchsia Rust, a fungal infection - it starts out with orange spots, and over time, the leaves yellow and develop black spots. RHS info about it here

https://www.rhs.org.uk/advice/profile?pid=163

I hope this cheers you up a bit Barbara:

I see this on some of mine every year so I've been out to examine a few leaves under a magnifier. I couldn't see any signs of a fine brown powder on the reverse of the leaves though they do look like the ones on Bamboo's link.. (I did see the rust powder on the backs of leaves of some newly acquired young plants once but just took the leaves off. Those hadn't gone yellow at all.)

All I do is remove the affected leaves if and when I notice them, and the health of the plants has never been noticeably affected.

I'm sure there is no need at all to destroy the plants.

Thank you.
I have stripped the affected plants .They look sad spindles now but I have also used the fungicide recommended by RHS on remaining foliage. Given that they will lose their leaves soon when will it be safe to lift them (tender ones) and put in cold greenhouse over winter. (don't want to infect my grapevine and other tender overwintering plants)

I don't think Fuchsia rust affects other plants except for Abies and Epilobium, according to the RHS link - other rusts affect other plants.