The ionisation asymmetry is measured in a crossed-beam experiment utilising a W/EuS field emitter as a source of polarised electrons and dual-frequency optical pumping as the polarising process for the lithium atomic beam. The antiparallel-parallel asymmetry of the total ionisation cross section is positive with a broad maximum of 0.35 near threshold and a gradual decrease towards higher energies. A comparison is made with results of binary encounter and Born approximations. At threshold no significant variation of the asymmetry with energy is observed within a resolution of 0.3 eV.