  The surprising polarisation of Lambdas and other hyperons measured in many
unpolarised hadronic processes, p N --> Lambda X, has been a long standing
challenge for QCD phenomenology. One possible explanation was suggested,
related to non perturbative properties of the quark hadronisation process, and
encoded in the so-called Polarising Fragmentation Function (PFF). Recent Belle
data have shown a non zero Lambda polarisation also in unpolarised e+ e-
processes, e+ e- --> Lambda X and e+ e- --> Lambda h X. We consider the single
inclusive case and the role of the PFFs. Adopting a simplified kinematics it is
shown how they can originate a polarisation P_Lambda different from 0 and give
explicit expressions for it in terms of the PFFs. Although the Belle data do
not allow yet, in our approach, an extraction of the PFFs, some clear
predictions are given, suggesting crucial measurements, and estimates of
P_Lambda are computed, in qualitative agreement with the Belle data.
