Patio Plum OPAL very poorly

got this at start of spring from. Thompson and Morgan. It doubled in size but dear oh dear is it in bad shape. Whatever can i do please? I'd be gutted to lose it. Its like this all over.

 

To be honest. I can't say I have ever seen what might appear as a healthy plum tree. Possibly due to the texture of the leaves. Any ways. The foliage on your tree certainly is ailing. If possible, get rid of the most heavily affected leaves and burn them. Then as soon as the remaining leaves fall, gather them up and also burn them. Then as soon as the tree has entered it's dormant state. Tip it out. Thoroughly wash the roots and the container, if such is it's present home. Repot with 100% fresh compost. Dispose of the old compost as the fungal spores will survive in it.