An improved 'plug & play' interferometric system for quantum key distribution is presented. Self-alignment and compensation of birefringence remain, while limitations due to reflections are overcome. Original electronics implementing the BB84 protocol makes adjustment simple. Key creation with 0.1 photon per pulse at a rate of 325Hz with a 2.9% QBER, corresponding to a net rate of 210Hz, over a 23km installed cable was realised.