  We present optical, near-infrared and radio observations of the 3-hour field
of the Canada-UK Deep Submillimetre Survey. Of the 27 submillimetre sources in
the field, nine have secure identifications with either a radio source or a
near-IR source. We show that the percentage of sources with secure
identifications in the CUDSS is consistent with that found for the bright `8
mJy' submillimetre survey, once allowance is made for the different
submillimetre and radio flux limits. Of the 14 secure identifications in the
two CUDSS fields, eight are VROs or EROs, five have colours typical of normal
galaxies, and one is a radio source which has not yet been detected at
optical/near-IR wavelengths. Eleven of the identifications have optical/near-IR
structures which are either disturbed or have some peculiarity which suggests
that the host galaxy is part of an interacting system. One difference between
the CUDSS results and the results from the 8-mJy survey is the large number of
low-redshift objects in the CUDSS; we give several arguments why these are
genuine low-redshift submillimetre sources rather than being gravitational
lenses which are gravitationally amplifying a high-$z$ submillimetre source. We
construct a $K-z$ diagram for various classes of high-redshift galaxy and show
that the SCUBA galaxies are on average less luminous than classical radio
galaxies, but are very similar in both their optical/IR luminosities and their
colours to the host galaxies of the radio sources detected in $\mu$Jy radio
surveys.
