Many thanks to all of you who have responded - with a special mention to nevets88. When you say
'Don't just blindly hit balls. You should know what you're trying to do before you hit a ball. For example, I know that for me, I like to do the following/have these feelings on approach shots: good setup, preset forward lean, face pointed at 0*, move off the ball some with my left shoulder, feel the club head hinge up vertically, and then on the downswing make the head "whoosh" and hit the ground after the ball at the same time.'
I would say that's pretty much exactly what I do in both practice, and on the course in my 'practice shots' - where it all works and feels fine. I'm not saying I always make a great shot - sometimes my timing or control is out and I make poor contact, hit it thin or fat etc - but the point is my body is doing approximately what I want it to. When I'm on the fairway for real, with the ball there, I can feel it's wrong as soon as I start my backswing - it's as though it's having a spasm and I just can't repeat the action. It's nothing to do with the lie - we have a practice ground where I can stand in short rough on a slope and still make my 'good' (ie intended) swing.
I've just been reading up on the yips - which are described as
a "brain spasm that impairs the short game." and a "focal dystonia," a neurological condition that provokes involuntary movements around specific actions
This sounds spot on except it's my long game that's affected. I've also realised that it's nowhere near as bad on my shorter clubs (anything from my 26 degree hybrid down) where I'm only slightly affected - but my longer clubs and driver are hopeless. So I'm now thinking it is actually a version of the yips. Does that sound nuts?
I had the same issue with my left elbow, physiotherapist treatment worked for me to reduce the pain. Then strengthen the forearms and wrists, I'm stronger and pain free and enjoy hitting a golf ball, I looked online for golf stretch and strengthen exercises and now have a routine that helps me. Good luck...