Fusion produced alpha particles may spontaneously enhance the stability of an ignited plasma against m = 1 internal modes. Stable values of the peloidal beta of the thermal plasma component significantly in excess of the ideal MHD threshold can be attained, provided the region where the magnetic helical parameter q is below unity is not too wide and the ignition temperature is not too high. A comprehensive analysis of the different instability regimes is presented, with special attention to so-called "fishbone oscillations" and their influence on the ignition energy balance. The theoretical predictions compare favourably with sawtooth suppression experiments in JET with high power ion cyclotron resonant frequency heating, where energetic ions in the MeV range are produced.