Can you record a video of this happening so I can understand better?
Because
" when I get to the final approach (whether I have had to turn back around for final or not - although seems worse when I have to do a u-turn). The plane is quite a bit off - like the green LOC line is half way between the middle and the outside of the circle."
Sounds like you just haven’t set the right inbound course on a CDI, or haven’t completely intercepted the localiser.