Spray with an anti fungal treatment for rust/mildew.

I'll respond here - couldn't recall which question yours was from the PM. You've not said which variety of Euphorbia it is - some have two lots of stems, those produced last year and which have flowered this year, coupled with new stems ready for flowering next year. Do not cut the new growth if that's the kind of plant you have. Use the spray - choose a systemic one and spray fortnightly or follow the instructions on the bottle. Not a good idea to cut down now, its a bit late in the season, but if you have the kind with flowered stems and new growth, cut out the flowered stems now.
You can respond underneath here, as if you're answering your own question, if you need to.

Hi there thank you for your help so far i only joined this site this morning so im trying to find my way around
I think my plant is a :-
Euphorbia characias wulfenii * Mediterranean Spurgeth, its pale greeny grey in colour and flowers it has the milky sap if cut , i would attach a picuture if in knew how but i will get a rust spray in the meantime and wont cut anything back yet , some leaves have fallen off but im worried about it infecting other plants , it sits next to a very large Fatsia which i dont want to loose either

thanks again

i think ive managed to up load a picture :-), this is a simular type to mine

If it is the one you named above, then it has biennial stems, as I mentioned above. Inspect the plant thoroughly - you're looking for new, smaller growth in the form of individual stems coming up from the base. If they are present, then cut out the flowered stems (if the flowers have finished, if not, wait till they have). And spray, of course. Fatsia is not particularly prone to mildew or rust attack.

Great i shall get on it right away thank you so much this has been so helpful