[en] Simultaneous target and projectile single ionization in 3.6 MeV u^-1 C²⁺ + He collisions is considered, within a six-body classical trajectory Monte Carlo model. Analysis of the relative azimuthal angle between the two emitted electrons allows one to discriminate the ionization contribution produced by the two-centre dynamical electron-electron interaction from that due to nucleus-electron interactions. The present calculations agree well with cross section measurements recently performed in kinematically complete experiments. (letter to the editor)