Kata-soto-ashi-dori is new to the BJA syllabus, more of a better classification than previously. The Kodokan do not refer to any ashi-dori, instead refer to morote-gari, which in this terminology would be considered morote-ashi-dori, I'd imagine. Either that, or the Kodokan would consider this a version of kibisu-gaeshi.
So looking at the technique, 'ashi-dori' is 'leg-grab' -the use of 'kata' in this sense is actually for 'single', rather than the other meanings of 'forms' or 'shoulders'. So, for this relatively simply technique, the name is the most difficult barrier in my honest opinion.
To perform this technique, keep hold of the collar with your tsuri-te, your other hand grabbing the outside of your partners leg and lifting, driving backwards with your tsuri-te.
