  We use the final data from the VIPERS redshift survey to extract an
unparalleled sample of more than 2000 massive M > 10^11 M_sun passive galaxies
(MPGs) at redshift 0.5 < z < 1.0, based on their NUVrK colours. This enables us
to investigate how the population of these objects was built up over cosmic
time. We find that the evolution of the number density depends on the galaxy
mean surface stellar mass density, Sigma. In particular, dense (Sigma > 2000
M_sun pc^-2) MPGs show a constant comoving number density over this redshift
range, whilst this increases by a factor ~ 4 for the least dense objects,
defined as having Sigma < 1000 M_sun pc^-2. We estimate stellar ages for the
MPG population both fitting the Spectral Energy Distribution (SED) and through
the D4000_n index, obtaining results in good agreement. Our findings are
consistent with passive ageing of the stellar content of dense MPGs. We show
that at any redshift the less dense MPGs are younger than dense ones and that
their stellar populations evolve at a slower rate than predicted by passive
evolution. This points to a scenario in which the overall population of MPGs
was built up over the cosmic time by continuous addition of less dense
galaxies: on top of an initial population of dense objects that passively
evolves, new, larger, and younger MPGs continuously join the population at
later epochs. Finally, we demonstrate that the observed increase in the number
density of MPGs is totally accounted for by the observed decrease in the number
density of correspondingly massive star forming galaxies (i.e. all the
non-passive M > 10^11 M_sun objects). Such systems observed at z ~ 1 in VIPERS,
therefore, represent the most plausible progenitors of the subsequent emerging
class of larger MPGs.
