  We study inflationary scenarios driven by a scalar field in the presence of a
non-minimal coupling between matter and curvature. We show that the Friedmann
equation can be significantly modified when the energy density during inflation
exceeds a critical value determined by the non-minimal coupling, which in turn
may considerably modify the spectrum of primordial perturbations and the
inflationary dynamics. In particular, we show that these models are
characterised by a consistency relation between the tensor-to-scalar ratio and
the tensor spectral index that can differ significantly from the predictions of
general relativity. We also give examples of observational predictions for some
of the most commonly considered potentials and use the results of the Planck
collaboration to set limits on the scale of the non-minimal coupling.
