Many thanks for your help. Ok it seems that I shouldn't be too concerned.
I am not an experienced gardener, so I appreciate the tips you've given me, particularly the time to prune as that would have been my next question for the forum!! Should I prune once per year only, early summer?
The black patches in Photinia leaves are caused by Entomosporium maculatum, a fungal leaf spot disease. It's is very common and is not harmful to the shrub. The main reason of these spots occurring, is the leaves remaining wet over a long period. It doesnt look very nice though.
Plants in a sheltered spot are more prone to leaf spots, as well as new foliage. Pruning during the growing season will encourage new growth. Mature leaves are more resistant to leaf spot.
If nothing seems to work, you can try spraying with a fungicide just before and during new foliage is emerging. If that doesn't make any difference, I would be inclined to remove Red Robin althogether.
I hope this will help.
My red robin leaves appear to be turning black, and going crumbly on the ends as if they have been burnt,
can anyone offer any advice ???