Thanks for all the comments, been having a think and also watching clips of some players on YouTube (not that I want to or have any chance of batting like them). I reckon my problems are a mix of issues. My eyes might not be level in my stance, I'm sure I am driving at balls I should be blocking and I think my backlift doesn't help.
With my backlift I try to have the bat straight behind me facing the deck. I think I'd always assumed this would help me come down straight but I suspect my bat is drifting behind me towards leg and meaning I come down in an arc, most likely this could contribute to missing stuff on leg and also explain why I drag balls to leg. Watching videos a lot of players seem to have a backlift towards the slips but still come down straight.
In nets tomorrow I plan to work on a different backlift, keeping my stance as still as possible with eyes level and balanced on the balls of my feet.
Thanks again