Hey, thanks for the speedy reply!

I tried all those things and they didn't work at first however after a bit of fiddling I managed to fix it.

It was caused by half of the normals (the ones on the right in the image) being reversed.
To identify this I turned off double sided in the attribute spreadsheet and selected all of the invisible faces then reversed the normals.
Once this was done I selected the entire mesh (Not just the hard edges) and softened the normals.

Hopefully if anyone else has this problem this'll help em out. I've lost count of how many times an 8 year old forum post has saved me hours of headaches lol.

Thanks for your help man, I probably would've given up by now..