  We present a near-infrared photometric search for unresolved substellar
companions and debris disks around white dwarfs in the UKIRT Infrared Deep Sky
Survey Large Area Survey. We cross-correlate the SDSS DR4 and McCook & Sion
catalogues of white dwarfs with the UKIDSS DR8 producing 3109 and 163 unique
matches respectively. Cooling models are fitted to the optical photometry of a
subsample of DA white dwarfs and extended to the near-infrared. A comparison is
then made with the observed photometry to identify those stars with a
near-infrared excess consistent with the presence of a cool companion or debris
disk. Where present, we have estimated the approximate spectral type of any
putative companion, or an upper limit on the temperature of a debris disk. In
total we identify 14-16 new candidate white dwarf + very low mass stellar
systems, 9-11 candidate white dwarf + brown dwarf systems, and 3 candidate
white dwarf + debris disks. We place lower limits on the unresolved (<2")
companions to all DA white dwarfs and thus assess the sensitivity of UKIDSS to
such objects. We use this result to estimate unresolved binary fractions of
f(WD+dL)>0.4+/-0.3%, f(WD+dT)>0.2% and f(WD+BD)>0.5+/-0.3%.
