Chlorine is produced by electrolysis of aqueous HC1, in a membrane electrolyzer, using cathodic mediators such as Fe(III) and/or Cu(II) chlorides and a non-catalysed 3-dimensional cathode, with the real surface area at least ten times higher than its projected area. The HCl electrolysis section is combined with an oxidiser for regeneration of the mediator, product water removal step and optional HCl recovery step. Under optimised conditions chlorine can be produced at very high current densities of 30 kA/m2, without initiating undesired H2 evolution reaction at the cathode.