In the search for new multiferroic materials, the class of ferroelectrics in which electronic polarisation is driven by a process of charge ordering is of prime interest. Among them is LuFe2O4, for which the origin of the electric properties is still a matter of speculations. The understanding of the coupling between electronic and magnetic degrees of freedom is in fact complicated by the complex magnetic ground state which involves phase competition due to ferro/antiferromagnetic coupling intra/inter bilayers. This peculiar state is probably at the basis for the unusual temperature dependence of the magnetic behaviour and in particular for the giant coercivity, attracting currently so much attention. Neutron diffraction under magnetic field appear thus as the unique tool to clarify the complex magnetic phase diagram of LuFe2O4.