Experiments and modelling have been carried out in order to optimize the magnetic field null during breakdown at JET. Such optimization may prove to be essential to reliable plasma initiation at low voltage, e.g. in ITER where the value of the electric field available will be limited to 0.33V/m. A 2 dimensional FEM electromagnetic model has been employed to predict the stray field configuration during JET breakdown. This model includes the active Poloidal Field (PF) circuits, a description of the passive structure and the JET magnetic circuit. In particular the model includes the gap in the top of the iron circuit (but not at the bottom) which introduces a perturbing field, with radial and vertical components, not previously considered. A number of experiments were run by using the optimised magnetic null configuration, allowing to achieve a more robust breakdown at low electric field. The model predictions were validated by using the recordings from the fast visible camera. The optimised position and dynamics of the plasma start lead to a smoother behaviour of the JET radial field control system, far from the amplifiers limits. Finally, an important indication was obtained on the precision needed for the active currents measurements during the low electric field breakdown relevant in perspective of the ITER real-time acquisition system.