plant leaves , discoloured

We have a large garden in south cumbria . We had a wet may , and warm dry june , july , only two days rain . We have a variety of mature shrubs in pots and the open ground . The leaves on these plants ( viburnams , philadelphus, roses , peony , and more  ) have got lime green blotches on the older leaves and it is getting worse . Please any ideas as to what this is , and a solution ??
Regards 
Roy