We wish to probe the suggested existence of a high-temperature cubic perovskite phase in the multiferroic material BiFe0.7Mn0.3O3. The parent phase of this material, BiFeO3, was previously also thought to possess a cubic phase over a very narrow temperature interval around 930 C, undergoing a simultaneous electronic transition. However, our recent HRPD studies have unambiguously shown this claim to be incorrect, and BiFeO3 remains orthorhombic above the electronic transition. The recent report of a similar transiiton sequence in this Mn-doped derivative phase, but with a much wider and therefore more accessible temperature window for the suggested cubic phase, allows an ideal opportunity to see whether this elusive 'cubic' phase truly exists. High resolution PND is the proven optimal techniuqe to study this possibility.