  The vector-tensor (VT) theory of gravitation revisited in this article was
studied in previous papers, where it was proved that VT works and deserves
attention. New observational data and numerical codes have motivated further
development which is presented here. New research has been planed with the
essential aim of proving that current cosmological observations, including
Planck data, baryon acoustic oscillations (BAO), and so on, may be explained
with VT, a theory which accounts for a kind of dark energy which has the same
equation of state as vacuum. New versions of the codes CAMB and COSMOMC have
been designed for applications to VT, and the resulting versions have been used
to get the cosmological parameters of the VT model at suitable confidence
levels. The parameters to be estimated are the same as ingeneral relativity
(GR), plus a new parameter $D$. For $D=0$, VT linear cosmological perturbations
reduces to those of GR, but the VT background may explain dark energy. The fits
between observations and VT predictions lead to non vanishing $|D|$ upper
limits at the $1\sigma $ confidence level. The value $D=0$ is admissible at
this level, but this value is not that of the best fit in any case. Results
strongly suggest that VT may explain current observations, at least, as well as
GR; with the advantage that, as it is proved in this paper, VT has an
additional parameter which facilitates adjustments to current observational
data.}
