The structures of ion conducting mixed-alkali metaphosphate glasses (A(2)O)(x)-(B2O)(1-x)-P2O5 (A,B = Li,Na,Rb) have been examined by neutron diffraction and Raman spectroscopy. The results show that the short range order of the phosphorous-oxygen network is almost independent of the composition. The length-scale of the intermediate range order correlations increases with increasing size of the cation. For all the investigated compositions the nearest Li-O, Na-O and Rb-O distances have been estimated from the atomic pair correlation functions to be 2.0+/-0.1, 2.35+/-0.1 (Na-O I), 2.6+/-0.1 (Na-O II) and 2.9+/-0.1 Angstrom, and the corresponding average coordination numbers are approximately 4, 3 (I) + 2.5 (II) and 5, respectively. Thus, the cation environments are distinctly different for Li+, Na+ and Rb+ and each of them remain the same for all compositions within experimental errors. The alkali ions are quasi-uniformly distributed and we were not able to observe any significant preference for either similar or dissimilar pairs. This implies that the mixed-alkali effect can be qualitatively understood on a purely structural basis. The A sites are energetically unfavourable to the B+ ions (and vice versa) and jumps to dissimilar sites are then unlikely to occur. Thus, the A sites will have the tendency of blocking the pathways for the B+ ions and vice versa.