  We discuss the potential to constrain the small-$x$ PDFs using the exclusive
production of heavy vector mesons. The calculation of $J/\psi$ and $\Upsilon$
photoproduction at NLO in collinear factorisation is described. The different
behaviour of the NLO corrections for $J/\psi$ and $\Upsilon$ is highlighted and
we outline what might be expected from the inclusion of these processes in a
PDF fit.
