The present invention relates to a novel method of flame retarding a polymeric substrate by adding a small but efficient amount of a synergistic mixture of at least one sterically hindered N-alkoxyamine (NOR), at least a metal salt of hypophosphorous (phosphinic) acid and at least one organo-halogen flame retardant. A further aspect of the invention is the flame retardant composition itself and together with a polymer. The present invention also relates to polymeric articles (e.g. moldings, films, fibers, etc.) that are stabilized against light, heat and oxygen and made flame retardant by incorporation of at least one sterically hindered N-alkoxy amine, at least a metal salt of hypophosphorous acid (phosphinic acid) and at least one organo-halogen flame retardant.