  Constraints on the Galactic bulge/bar structure and formation history from
stellar kinematics and metallicities mainly come from relatively high-latitude
fields (|b|>4) where a complex mix of stellar population is seen. We aim here
to constrain the formation history of the Galactic bar by studying the radial
velocity and metallicity distributions of stars in-situ (|b|<1). We observed
red clump stars in four fields along the bar's major axis (l=10,6,-6 and b=0
plus a field at l=0,b=1) with low-resolution spectroscopy from VLT/FLAMES,
observing around the CaII triplet. We developed robust methods for extracting
radial velocity and metallicity estimates from these low signal-to-noise
spectra. We derived distance probability distributions using Bayesian methods
rigorously handling the extinction law. We present radial velocities and
metallicity distributions, as well as radial velocity trends with distance. We
observe an increase in the radial velocity dispersion near the Galactic plane.
We detect the streaming motion of the stars induced by the bar in fields at
l=+/-6, the highest velocity components of this bar stream being metal-rich
([Fe/H]~0.2 dex). Our data is consistent with a bar inclined at 26+/-3 from the
Sun-Galactic centre line. We observe a significant fraction of metal-poor
stars, in particular in the field at l=0,b=1. We confirm the flattening of the
metallicity gradient along the minor axis when getting closer to the plane,
with a hint that it could actually be inverted. Our stellar kinematics
corresponds to the expected behaviour of a bar issued from the secular
evolution of the Galactic disc. The mix of several populations, seen further
away from the plane, is also seen in the bar in-situ since our metallicity
distributions highlight a different spatial distribution between metal-poor and
metal-rich stars, the more metal-poor stars being more centrally concentrated.
