  We have undertaken a pilot survey for faint QSOs in the UKIDSS Ultra Deep
Survey Field using the KX selection technique. These observations exploit the
very deep near-infrared and optical imaging of this field from UKIRT and Subaru
to select candidate QSOs based on their VJK colours and morphologies. We
determined redshifts for 426 candidates using the AAOmega spectrograph on the
AAT in service time. We identify 17 QSOs (M_B<= -23) in this pilot survey at
z=1.57-3.29. We combine our sample with an X-ray selected sample of QSOs in the
same field (a large fraction of which also comply with our KX selection) to
constrain the surface density of QSOs with K<=20, deriving limits on the likely
surface density of 85-150/deg^2. We use the good image quality available from
our near-infrared imaging to detect a spatially extended component of the QSO
light which probably represents the host galaxies. We also use our sample to
investigate routes to improve the selection of KX QSOs at faint limits in the
face of the significant contamination by compact, foreground galaxies. The
brightest examples from our combined QSO sample will be used in conjunction
with a large VLT VIMOS spectroscopic survey of high redshift galaxies in this
region to study the structures inhabited by gas, galaxies and growing
super-massive black holes at high redshifts in the UKIDSS UDS.
