Experiments in the JET Tokamak with additional heating power (ion cyclotron resonance heating and/or neutral beam injection) above 5MW show that the plasma can undergo a sudden transition to a new regime in which the sawtooth instability is suppressed for periods of up to 1.6s and the level of long wavelength, coherent mhd activity is very low. Possible mechanisms for the observed stabilization of the m=1 instability and the potential gains in the near ignition regime are discussed.