The linear stability of ideal instabilities with low toroidal mode numbers has been assessed for various high beta plasmas in JET with the minimum in safety factor near 1, 3/2 and 2. In all cases, the plasmas are found to become unstable to global ideal kink-ballooning modes as the minimum safety factor approaches rational values. The plasmas are found to exhibit continuous modes experimentally which degrade performance, with the mode onset being extremely well correlated to the crossing of the numerically-predicted stability boundaries. The most favourable profiles for global stability have also been assessed.