  We report on two new XMM-Newton observations of the Anomalous X-ray Pulsar
(AXP) 4U 0142+614 performed in March and July 2004, collecting the most
accurate spectrum for this source to date. Furthermore, we analyse two short
archival observations performed in February 2002 and January 2003 (the latter
already reported by Gohler et al. 2005) in order to study the long term
behaviour of this AXP. 4U 0142+614 appears to be relatively steady in flux
between 2002 and 2004, and the phase-averaged spectrum does not show any
significant variability between the four epochs. We derive the deepest upper
limits to date on the presence of lines in the 4U 0142+614 spectrum as a
function of energy: equivalent width in the 1-3 keV energy range < 4 eV and < 8
eV for narrow and broad lines, respectively. A remarkable energy dependence in
both the pulse profile and the pulsed fraction is detected, and consequently
pulse-phase spectroscopy shows spectral variability as a function of phase. By
making use of XMM-Newton and INTEGRAL data, we successfully model the 1-250 keV
spectrum of 4U 0142+614 with three models presented in Rea et al. (2007a),
namely the canonical absorbed blackbody plus two power-laws, a resonant
cyclotron scattering model plus one power-law and two log-parabolic functions.
