I've spotted this for sale
A WS Manufacturing Ltd No.A5 plane with a corrigated base. Does anyone know if WS made them this way, or are the corrigations a user mod?
I've never seen a corrugated WS, but I've never seen that many WS bench planes at all.
Most of the "other" brands tended to make most of the Stanley models, and making the grooves (neatly) would be quite a trick for a user, especially one who's a woodworker, not a metal worker.
So (on balance of present evidence) I'd call it original.