  We propose a simple mechanism which enforces |U_{mu j}| = | U_{tau j}| forall
j = 1,2,3 in the lepton mixing matrix U. This implies maximal atmospheric
neutrino mixing and a maximal CP-violating phase but does not constrain the
reactor mixing angle theta_{13}. We implement the proposed mechanism in two
renormalizable seesaw models which have features strongly resembling those of
models based on a flavour symmetry group Delta(27). Among the predictions of
the models, there is a determination, although ambiguous, of the absolute
neutrino mass scale, and a stringent correlation between the absolute neutrino
mass scale and the effective Majorana mass in neutrinoless double-beta decay.
