This paper discusses the power step-down approach to steady-state operation of deuterium plasmas in the hot-ion ELM-free H-mode of the JET tokamak. Being ELM-free, when full heating power is maintained, these plasmas are usually transient and terminate with a variety of MHD phenomena. With power step-down, instabilities are delayed or avoided and nearly constant plasma conditions at up to 10MJ of stored energy are maintained by 10MW of heating power for up to 1s, about an energy confinement time at 3.5MA and 3.4T. Global ELM-free H-mode confinement scaling is examined in this regime, without recourse to large transient corrections. The confinement times increase after the transition to quasi-steady conditions, and are some 10-25% above the scaling law predictions, with the same parametric dependence. Code simulations of the experimentally observed neutron rate and the lack of a major discontinuity in the rate before and after power step-down confirm that neutron production is predominantly (>60%) from thermal fusion. The scaling of fusion rates from deuterium plasmas to deuterium-tritium mixtures implies a fusion Q approaching 1, and alpha particle heating which exceeds beam heating and ion-electron exchange in the core electron power balance. The constant edge pressure gradient contributes to the improved edge mode stability of these discharges. The Giant ELMs which usually terminate the discharge seem to be the result of a slowly evolving current density profile. Optimisation experiments indicate that the stored energy and neutron production are maximised and the density rise minimised by preferentially retaining the JET high energy 140keV beams. The plasma remains in an ELM-free H-mode even when the heating power after step-down is lower than the L-H transition power. Thus, the power step-down method provides a significant advance towards the regime of steady-state high performance and will be utilised in future D-T experiments.