Having filmed my swing using slow-mo on my camera and showing it to my mate, his response was:
"That my friend is what we call a classic chicken wing".
So then he told me to watch this video to help understand how to release properly:
The thing I am finding at the moment is that so much advice from people and videos is completely overwhelming, contradictory, conflicting and confusing.
People will tell me my swing is too "wristy" which I totally get, and to keep my arms straight. Yet you have to move your wrists to swing a club. You also have to bend your arms after release or it's painful. I think it has highlighted to me that the only way to progress right now for me is to get lessons with an actual pro who can make adjustments in person. You can't really see what you are doing yourself without constantly filming and reviewing it.
The thing Mark talks about in the above video at 3:50 onwards I find strange, because the actual drill and position he is trying to get you into is not very much like what happens in a full swing. He even says to pull the handle up and around the waist but in the drill it's miles out in front of him. I guess for demo purposes.
I have also struggled with the whole "get your hands forward" for iron shots so you hit down on the ball more, only to see videos saying basically the complete opposite to not pull the handle through too far like a cricket bat shot, as this will introduce the chicken wing.
With all the above in mind. I spent some time in the garden yesterday just hitting air and trying to shape my swing a bit more. I've found that I can prevent the left arm chicken wing by locking/stretching out my left arm and really focussing on keeping it straight. The club head then finishes not so rolled round to close, which is good, but... this kind of feels almost painful. I gather the arms are meant to be loose-ish. I also have a very strong grip. A coach once told me my grip was fine and not to focus in on it, yet when I mad minor adjustments in the garden yesterday rolling the left hand under more, it seemed to help a bit.
TLDR - waffle and moan about a bad swing.