The possibility that the loss of resonant ion confinement during the sawtooth crash may be due to fast radial diffusion driven by a kink type of instability within the plasma core is considered. Starting from a simplified model of a helically distorted toroidal magnetic field and assuming the ions to be confined to the q < 1 region of the plasma, where q is the safety factor, a diffusion coefficient is obtained. Then by assuming that the resonant ion tail formation and relaxation processes are classical, the time development of the fast ion energy content of the plasma is modelled. Finally, an estimate of the loss of fast ions from the plasma core during the crash is given for a typical JET ICRH discharge and the fraction of ions ejected from the core is obtained by direct comparison with experimental data.