Fibre measurement of key parameters in nuclear fusion reactor environments, such as the magnetic field strength and temperature, is highly desirable due to the convenience and robustness of optical fibre sensors when compared with conventional electrical sensors. Presently, fibre point sensors for magnetic field are based predominantly on magnetostriction which limits their applicability to this environment. We present an optical fibre sensor system that is purely magneto-optical and capable of simultaneous interrogation for magnetic field strength and temperature at a number of points along a single fibre. Fibre Bragg gratings written with low linear birefringence are utilised as multiplexable transducers that can be decoded using a novel polarisation-switching interrogation system. Here we report on the design and simulation of this system and use preliminary results to demonstrate its capability for measurement of both magnetic field and temperature simultaneously. Additionally we report on the resolutions possible using the present laboratory embodiment, and discuss how they may be improved upon in future embodiments incorporating the novel differential measurement technique detailed herein.