I would look at the undersides of the leaves for evidence of scale or mealybugs. The first that you see of them is frequently small yellow spots on the upper side.

I think you will find the the yellow leaf spotting is a rust. You will need to cut off the lowest leaves (not all of them at once) and spray with a fungicide. The older leaves do not tend to recover and seem to be permanently spotted but the new leaves will eventually take over as you cut off the older ones. A common problem and most noticeable on the green varieties.

Ah! Good to know!

Thank you very much for your replys much appreciated.