Thanks to all for your help. It turned out to be a combination of different issues. I've since upgraded the tube to 120w so I don't have to push it so hard, also stiffened up the Y axis (got rid of the plastic wheel that was on one side and replaced with a linear bearing), realigned and cleaned all the mirrors, realigned the z bed and now the cut quality is much improved.
Oh, and I also focus further down into the material too.

Many thanks 👍