  We present maps of the 850 micron and 450 micron continuum emission seen
towards a sample of 68 high-mass protostellar candidates with luminosities
ranging from 10^2.5 to 10^5 solar luminosity. Most of these candidate high-mass
stars are in the earliest stages of evolution, and have not yet developed an
ultra-compact HII region. We observe a variety of continuum emission
morphologies, from compact symmetric sources through to multiple cores embedded
in long filaments of emission. We find on average there is a 65% probability of
an IRAS point-source having a companion detection at submillimetre wavelengths.
The ratio of integrated flux to peak flux for our detections shows no strong
dependence on distance, suggesting the emission we have observed is primarily
from scale-free envelopes with power-law density structures. Assuming a near
kinematic distance projection, the clumps we detect vary in mass from ~1 to
over 1000 solar mass, with a mean clump mass of 330 solar mass, column density
of 9x10^23 cm^-2 and diameter of ~0.6 pc. The high luminosity and low mass of
the smallest clumps suggests they are accompanied by a minimal number of
stellar companions, while the most massive clumps may be examples of young
protogroups and protoclusters. We measure the spectral index of the dust
emission (alpha) and the spectral index of the dust grain opacity (beta)
towards each object, finding clumps with morphologies suggestive of strong
temperature gradients, and of grain growth in their dense inner regions. We
find a mean value for beta of 0.9, significantly smaller than observed towards
UCHII regions.
