The role of fast particles in edge transport barrier formation is discussed. Analysis of recent experiments on JET that have been carried out in hydrogen, deuterium and tritium plasmas, and in a DT mixture, with NBI and ICRF heating is presented which supports the idea that the width of the edge transport barrier is controlled by the banana width of the fast beam ions in the case of NBI heating and by the banana width of the thermal ions in the case of ICRF minority heating. A simple theoretical model which can account for this effect is analysed.