We apply atomistic simulations to consider hydrogen behaviour in metals (Fe and Ni) in presence of the given lattice distortions, namely, crystal defects or lattice expansion/compression due to applied stresses. Simulations are based on a new interatomic potential developed by the authors of current work. We consider segregation of hydrogen on typical defects of different complexity: from vacancies to grain boundaries (GBs). Classical atomistic simulation, carried out in the spirit of a numerical experiment at a finite temperature, made it possible to obtain an equilibrium distribution of H in the presence of crystal defects. In addition, hydrogen diffusion in presence of GBs, surfaces, and vacancies was studied over a wide temperature range. Simulation results show that the interplay of H with defects depends significantly on the phase structure. For fcc-Fe, GBs provide an accelerating path for H diffusion. Conversely, GBs in bcc-Fe may retard H mobility compared to bulk case. The obtained results on H concentration and diffusivity at the defects were used to interpret existing experiments on H permeation in metals. In particular, for bcc Fe we show that GBs of the considered type do not act as diffusion accelerating channels. Based on this we may assume that the picture of H permeation observed in situ in some experiments, is probably a result coming from combination of fast H diffusion in bulk and strong segregation occurring at GBs.