Hi Jess, Thanks for that warning. I'll stick with SB Invigorator and ladybirds then for now and see how that works.
There are lots of different species of aphids and both sycamore and lupin have their own large aphid. These aphids are unlikely to feed on unrelated plants. The honeydew is produced by the aphids and falling onto your plants. The council are unlikely to spray the tree with pesticides but you could ask them to remove some of the lower branches.