Blackfly infestation on elderflower tree
I have a 20 ft high elderflower tree in my sunny little back garden in Bethnal Green, and as much as i enjoy having a tree - it is infested with blackfly from March - June usually, dropping tiny sweet sticky droplets over everything else including my clothes line and my neighbour's garden! I have tried spraying (first with washing up liquid solution, then reluctantly with bug killer), jet-spraying with the hose, and cutting it back as mcuh as possible, but new shoots come and the aphids seem to love these even more. What options do I have other than chopping it down? I hate to see the tree cut down, but i'm concerned both for the plants in my garden and my neighbours. Please help!
Grateful for any advice at all,