Here is a Spey cast I have not seen before. I think it is quite an innovative spin on the Double Spey, changing the Double Spey from a waterborne anchor cast to an airborne anchor cast. This cast has the potential to impart more energy to the D-Loop giving deeper loading and longer cast. It also has the potential to shake off some water from the fly before sending it on its way. This may be helpful in instances when we fish dry e.g. deer hair mouse, bomber etc. Note that this cast is kind of like doing a cack hand (or back hand) cast before commencing with the forehand cast.
Excerpt from Peter Anderson's comment in his video :
" The Enhanced Double Spey cast from Peter Anderson. It involves a back hand finishing movement on the first line placing part, this unrolls the fly line out in the air out over the river at a slightly downstream angle. The rod immediately follows round and then pulls the line back into a D loop on the downstream side. The cast has an airborne anchor. Ideal for a downstream wind that is also pushing out slightly from the anglers bank. On longer casts some line can be let slip out also if one wishes before pulling back into the D loop."