Sorry to hear that the methylated spirits isn't working, can only
suggest you keep at it. They over winter as aphids in the bark so
persistence is the key. The alcohol should be effective as it destorys
the eggs as well as killing the insects.
Are the aphids appearing around pruning cuts or other breaks in the
bark?
If so, after the meths has dried, apply a paste of Bordeaux mixture to
the cut. This will help to stop any secondary fungal infections -
particully canker.
The meths approach is far more effective than blasting the blighters
off with a jet of water, so I would stick with it.
Good luck
Clifford
Bawtry, Doncaster, South Yorkshire