Thanks for your replies, I’ve taken photos of the bridge. Most of the saddle screws are screwed in about halfway down the hole, it doesn’t seem it will get much higher. Most of the strings seem to buzz at the 20th or 21st fret, the action is extremely low.
I do have one of those rulers around that I can check this with, it maybe that I need to set the truss rod correctly.
I will also recheck the neck attachment as Simon mentioned. On another inspection by eye, it seems like the edge of the neck near the join seems a little higher off the body if that makes sense.