I am afraid, that it sounds like you need to intervene. You can either buy one of the many blackfly sprays, or make up a solution of washing up liquid and water. It sounds like there are too many to be squishing by hand.

Thanks, but the Plant is well over 10' tall, spraying with both once when it was smaller achieved nothing. The others are hardly touched, its just this one that has always really suffered. These 'aphidy things' are grey, I have assumed they are not actually blackfly. Is this particular plant just too susceptible does anybody know?

Hmmm.... That does make it difficult. Maybe someone else will be able to give you an answer.

I am sorry I could not assist further.

Thanks Alextb, appreciate your taking the time, anyway.

Are these very pale gray, almost white, and fuzzy looking? They may be wooly aphids or mealybugs, both of which are more resistant to sprays than regular aphids. You can still use the soapy water, but you will need to spray unusually thoroughly, frequently, and persistently. The oily wool that they are covered with keeps most sprays from penetrating far. I would use an organic washing up liquid, to prevent toxic reactions in the soil, later. Mix it up around 2 tablespoons per liter, which is a little stronger than usual. Then spray to the point of runoff. Repeat every three days until they give up, which may take over a month.

The colouration could be as you suggest but I can't get nearer to confirm after yesterday's heavy rain, it appears to have washed them off. Two picky's of the plant are now on here. As well as some fresh new growth that will very shortly become affected, you can see mostly the damaged leaves and buds. I have tried aphid spray and washing up water in previous years, but whatever the condition is, it is really getting the better of me and the plant. Could the bugs/condition be connected with the coniferous hedge, which may be why the plant and I are losing the battle.

Well, the little that I was able to see did look a lot like severe aphid--or mealybug, or scale--damage If the rain actually did wash them off, it should now begin to recover, especially if you apply a gentle fertilizer, such as growmore. That may be doubly important next to that conifer, since it is going to suck most of the nutrients out of the ground, too. I would also check to see how much shade it is getting, since it also looks suspiciously etiolated.