I bought a long allen key for £3 from Amazon, and have adjusted the lights every few days, upwards,  one turn each side, then tested it.  After 4.5 turns up, the lights seem perfect, clipping a flat road about 150 ft in front of the car.
Note there are two white adjusters, the up / down one is much lower down behind the light cluster than the upper R/L one. 
Many thanks for the idea.