  We present the results of a deep wide-field near-infrared survey of 12 square
degrees of the Pleiades conducted as part of the UKIDSS Deep Infrared Sky
Survey (UKIDSS) Galactic Cluster Survey (GCS). We have extracted over 340 high
probability proper motion members down to 0.03 solar masses using a combination
of UKIDSS photometry and proper motion measurements obtained by
cross-correlating the GCS with data from the Two Micron All Sky Survey (2MASS),
the Isaac Newton (INT) and the Canada-France-Hawai'i (CFHT) telescopes.
Additionally, we have unearthed 73 new candidate brown dwarf members on the
basis of five band UKIDSS photometry alone. We have identified 23 substellar
multiple system candidates out of 63 candidate brown dwarfs from the (Y-K,Y)
and (J-K,J) colour-magnitude diagrams, yielding a binary frequency of 28-44% in
the 0.075-0.030 Msun mass range. Our estimate is three times larger than the
binary fractions reported from high-resolution imaging surveys of field
ultracool dwarfs and Pleiades brown dwarfs. However, it is marginally
consistent with our earlier ``peculiar'' photometric binary fraction of
50+/-10% presented in Pinfield et al. (2003), in good agreement with the 32-45%
binary fraction derived from the recent Monte-Carlo simulations of Maxted &
Jeffries (2005) and compatible with the 26+/-10% frequency recently estimated
by Basri & Reiners (2006). A tentative estimate of the mass ratios from
photometry alone seems to support the hypothesis that binary brown dwarfs tend
to reside in near equal-mass ratio systems. (abridged)
