Blue berries not blueberries!

I have absolutely no idea what plant these (berries!) belong to.  I spotted them this morning during my very brief visit to the pond in Maxwell Park. Near the entrance to the park there is a clump of rhododendron bushes (about 4ft high) and this sprig (one of two) was in among the bushes. Perhaps they belong to a species of rhododendron but I have certainly never seen them before.