The present invention provides flame retardant thermoplastic moulding compositions comprising: A) from 65% to 99.5% by weight (with respect of the total weight of the final composition) of a polyolefinic polymer particularly selected among polypropylene polymers; B) from 0.1% to 30% by weight (with respect of the total weight of the final composition) of a synergic mixture of an hypophosphorous acid metal salt and halogenated organic compounds; C) from 0.5% to 10% by weight (with respect of the total weight of the final composition) of a plurality of selected additives consisting of processing aids, heat and process stabilizers, UV stabilizers, antidripping agents (PTFE—Polytetrafluoroethylene), pigments, mould releasing agents, nucleating agents; D) from 0% to 50% by weight (with respect of the total weight of the final composition) of an inorganic filler. The total of the percentages by weight of components A to D is 100%.