Steady-state high performance with improved core confinement and sustainable plasma edge conditions has been approached on JET in a Double Barrier (DB) mode. The DB mode combines an internal transport barrier of the Optimised Shear regime with an edge transport barrier of an ELM&#180y H-mode regime. Improved confinement with an H-factor HITER-89 ≈ 2 has been maintained for four energy confinement times. Ion and electron temperature profiles remain peaked in the DB mode, while the density profile is broad and similar in shape to the ELM'y H-mode profile. The energy confinement improves across the whole plasma cross section, and the ion heat conductivity falls to the neo-classical level in the core. Particle transport studies show that impurity accumulation can be avoided in the DB mode. In deuterium-tritium discharges the DB mode has attained a fusion gain of Q ≈ 0.4, producing 6.8MW fusion power, compared with Q ≈ 0.2 in the conventional sawtoothing ELMy H-mode. The ELM's are more benign, with the amplitude an order of magnitude smaller in the Optimised Shear ELM&#180y H-mode. The DB mode has a high potential to improve performance in reactor relevant conditions.