Thanks for all the good feedback. Having read the posts I think I know what my problem is. Until now, my method has been:
1. Hit 50 balls...hmm, Not great. I must not be doing something the pros do in their swing. Solution - watch some videos and replicate.
2. Hit another 50 balls... Excellent. Something went well, figure out what I changed and exaggerate it.
3. Play 9 holes with my new pro swing. Think plane, think do not roll wrists, think left shoulder down, think...