Access to high bN regimes with a q profile compatible with large bootstrap current has been systematically investigated in JET H-mode plasmas. In these discharges with relatively broad pressure profile, the achievable bN was limited by an n=1 MHD instability that resulted in a soft but significant loss of confinement. Experiments have been performed with q95 5, as is envisaged for steady-state operation of ITER. bN values in excess of 3 have been achieved at qmin below 1.5, while at qmin close to 2 the beta-limiting mode occurred at lower values bN 2, as for the case shown in figures 2 and 3. The main features of the beta-limiting instability are: · At bN 2 the mode has kink-like structure at first, and develops an m = 2 island after 100-200 ms. Vice versa modes starting at bN < 2 have an island from the beginning. · Rotation frequency corresponding to plasma core toroidal rotation. · Presence of low-amplitude precursors, often in the form of fishbones. · Occurrence at bN values above the threshold for resonant field amplification.