The magnetoelectric Y-type hexaferrites demonstrate coupling between magnetism and electric polarisation in relatively small applied magnetic fields, and are hence candidate materials for use in future multifunctional devices. Of particular note is the observation that one can, without loss, invert the electric polarisation of the system with small magnetic fields - a non-trivial result that requires preservation of the antiferromagnetic domain structure throughout the switch. The magnetic mechanism that enables this inversion is not fully understood. In fact, suggested models are inconsistent with our initial observations. We propose to investigate this magnetic control of electric polarisation by performing a low field diffraction study on the WISH diffractometer. Understanding this phenomenon could in the future lead to novel methods of robust magnetoelectric switching.