  We derive the evolution of the ultraviolet upturn colour from a sample of
field luminous red galaxies at $0.3 < z < 0.7$ with $-24 < M_r < -21.5$. No
individual objects are securely detected, so we stack several hundred galaxies
within absolute magnitude and redshift intervals. We find that the colour of
the ultraviolet upturn (in observed $NUV-i$ which is approximately equivalent
to the classical $FUV-V$ at the redshifts of our targets) does not change
strongly with redshift to $z=0.7$. This behaviour is similar to that observed
in cluster ellipticals over this same mass range and at similar redshifts and
we speculate that the processes involved in the origin of the UV upturn are the
same. The observations are most consistent with spectral synthesis models
containing a fraction of a helium rich stellar population with abundances
between 37\% and 42\%, although we cannot formally exclude a contribution due
to residual star formation at the $\sim 0.5\%$ level (however, this appears
unlikely for cluster galaxies that are believed to be more quenched). This
suggests that the ultraviolet upturn is a primordial characteristic of early
type galaxies at all redshifts and that an unexpected nucleosynthesis channel
may lead to nearly complete chemical evolution at early times.
