PPL training does not have to be carried out AT a licenced airfield, it has to be carried out FROM a licenced airfield. There is nothing to stop confined area training from taking place off airfield so long as you do not physically touch down, and you are obeying the rule5 etc.
Confined area is in the syllabus and must be taught realistically, not with pretend trees to fly over. You can't let a fresh PPL go off flying into his back garden when he/she has never performed a confined area landing.