  Determining an accurate position for a submm galaxy (SMG) is the crucial step
that enables us to move from the basic properties of an SMG sample - source
counts and 2-D clustering - to an assessment of their detailed,
multi-wavelength properties, their contribution to the history of cosmic star
formation and their links with present-day galaxy populations. In this paper,
we identify robust radio and/or IR counterparts, and hence accurate positions,
for over two thirds of the SCUBA HAlf-Degree Extragalactic Survey (SHADES)
Source Catalogue, presenting optical, 24-um and radio images of each SMG.
Observed trends in identification rate have given no strong rationale for
pruning the sample. Uncertainties in submm position are found to be consistent
with theoretical expectations, with no evidence for significant additional
sources of error. Employing the submm/radio redshift indicator, via a
parameterisation appropriate for radio-identified SMGs with spectroscopic
redshifts, yields a median redshift of 2.8 for the radio-identified subset of
SHADES, somewhat higher than the median spectroscopic redshift. We present a
diagnostic colour-colour plot, exploiting Spitzer photometry, in which we
identify regions commensurate with SMGs at very high redshift. Finally, we find
that significantly more SMGs have multiple robust counterparts than would be
expected by chance, indicative of physical associations. These multiple systems
are most common amongst the brightest SMGs and are typically separated by 2-6",
or 15-50/(sin i) kpc at z ~ 2, consistent with early bursts seen in merger
simulations.
