  We investigate the production efficiency of ionizing photons ($\xi_{ion}^*$)
of 1174 galaxies with secure redshift at z=2-5 from the VANDELS survey to
determine the relation between ionizing emission and physical properties of
bright and massive sources. We constrain $\xi_{ion}^*$ and galaxy physical
parameters by means of spectro-photometric fits performed with the BEAGLE code.
The analysis exploits the multi-band photometry in the VANDELS fields, and the
measurement of UV rest-frame emission lines (CIII]$\lambda 1909$, HeII$\lambda
1640$, OIII]$\lambda 1666$) from deep VIMOS spectra. We find no clear evolution
of $\xi_{ion}^*$ with redshift within the probed range. The ionizing efficiency
slightly increases at fainter $M_{UV}$, and bluer UV slopes, but these trends
are less evident when restricting the analysis to a complete subsample at
log(M$_{star}$/M$_{\odot}$)$>$9.5. We find a significant trend of increasing
$\xi_{ion}^*$ with increasing EW(Ly$\alpha$), with an average
log($\xi_{ion}^*$/Hz erg$^{-1}$)$>$25 at EW$>$50\AA, and a higher ionizing
efficiency for high-EW CIII]$\lambda 1909$ and OIII]$\lambda 1666$ emitters.
The most significant correlations are found with respect to stellar mass,
specific star-formation rate (sSFR) and SFR surface density ($\Sigma_{SFR}$).
The relation between $\xi_{ion}^*$ and sSFR shows a monotonic increase from
log($\xi_{ion}^*$/Hz erg$^{-1}$) $\sim$24.5 at log(sSFR)$\sim$-9.5$yr^{-1}$ to
$\sim$25.5 at log(sSFR)$\sim$-7.5$yr^{-1}$, a low scatter and little dependence
on mass. The objects above the main-sequence of star-formation consistently
have higher-than-average $\xi_{ion}^*$. A clear increase of $\xi_{ion}^*$ with
$\Sigma_{SFR}$ is also found, with log($\xi_{ion}^*$/Hz erg$^{-1}$)$>$25 for
objects at $\Sigma_{SFR}>$10 M$_{\odot}/yr/kpc^2$.(Abridged)
