Multiferroic materials - those which exhibit spontaneous and switchable electrical and magnetic polarizations - have a wide range of applications. However preparing new magnetoelectric materials is challenging because ferroelectric and ferromagnetic properties are contraindicated. We have been working of a strategy of introducing magnetic behaviour to existing ferroelectric materials via topochemical cation exchange. Specifically, we are exploring the cation exchange chemistry of polar Dion-Jacobson and Ruddlesden-Popper phases to see if we can induce ferromagnetic behaviour whilst retaining the existing ferroelectric behaviour. We propose to collect high resolution neutron powder diffraction data from these exchanged phases, so we can determine their complex structural distortions, and thus determine if they retain their ferroelectric behaviour on cation exchange.