Ferroelectric tetragonal tungsten bronze oxides (TTBs) have been extensively studied for their application dielectric and non-linear optical devices. TTBs often exhibit structural (incommensurate) modulations which partially disrupt the long-range ferroelectric ordering and lead to relaxor behaviour. Recently we discovered a novel polar, commensurate TTB, Ba4La0.67Nb10O30, which displays relaxor behaviour. Electron diffraction shows that the oxygen positions are completely disordered; these local variations disrupt long range polar ordering resulting in a lack of macroscopic (ferroelectric) polarisation. Conventional diffraction analysis is insensitive to these local variations and so the aim of the current proposal is to probe the local structural variations as the material progresses from the relaxor to non-ferroelectric phase using total neutron scattering methods.