Thanks Fellas,
I think that on the course that I may be swinging from out to in or trying to steer the ball, but I don't do this at the range. The course has lots of trees and skinny fairways whereas at the range it quite open and I don't worry about the trees. I may also be tightening up under pressure of match conditions as it's a member only course and I play competition several times a week. I do get lessons, but the lessons are at the driving range, my instructor doesn't see me at the course so he doesn't see what changes. I think I'll need to have a game with my instructor on the course under match conditions.....