  In the framework of a flat FLRW model we derive an inflationary regime in
which the scalar field, laying on the plateau of its potential, admits a linear
time dependence and remains close to a constant value. The behaviour of
inhomogeneous perturbations is determined on the background metric in agreement
to the "slow-rolling" approximation. We show that the inhomogeneous scales
which before inflation were not much greater then the physical horizon,
conserve their spectrum (almost) unaltered after the de Sitter phase.
