IIRC, that was the old version Carrera. Many things have changed since, including the electronics (battery, controller, display... as well as the frame and mechanical parts).
Halfords choose electronics for their own ebikes which are pretty resiliant to punter fiddling. IIRC, the only successful modifications made to any of Halfords own-brand ebikes involved changing at least both the controller and display.
If you really want to cheat the UK limitations (250w/15.5mph/throttle etc), IMHO you'd really be better off starting with a different bike.