I think it might be wooly aphid and I presume you can get sprays for it.

Bad case of woolly aphid too. Sprays don't really work.
You need a Soap based spray which will dissolve the waxy coating (the wool). That exposes the aphid itself to the air and the insecticide.
Other way to attack is to spray the tree with a jet spray, not strong enough to damage the bark, but enough to wash off the bugs. they drown when the covering is removed.