Edge localized mode (ELM) control has been investigated on MAST with a set of in-vessel coils producing n = 3 perturbations. In spite of a broad enough region where the Chirikov parameter is above 1, according to the criterion employed for the design of the ITER ELM control coils, no effect was seen on type I ELMs. The behaviour on MAST is different from that in DIII-D in this respect. The coils do have an effect, however, on Ohmic L-mode plasmas and plasmas just above the L–H transition. In the former, they induce a density pump-out, modify the turbulence characteristics and edge radial electric field and produce a strike point splitting, while in the latter they can trigger ELMs in ELM-free plasmas.