  We present extensive observations of a sample of distant, submm galaxies
detected in the field of the massive cluster lens, A1835, using SCUBA. Taken in
conjunction with earlier observations of other submm-selected sources (Ivison
et al. 1998; Smail et al. 1999; Soucail et al. 1999) we now have detailed,
multi-wavelength observations of 7 examples of the submm population, having
exploited the combination of achromatic amplification by cluster lenses and
lavish archival datasets. These sources, all clearly at z > 1, illustrate the
wide range in the radio and optical properties of distant submm-selected
galaxies. We include detailed observations of the first candidate `pure'
starburst submm galaxy at high redshift, a z=2.56 interacting galaxy which
shows no obvious sign of hosting an AGN. The remaining sources have varying
degrees of inferred AGN activity (3 from 7 of the most luminous show some
evidence of the presence of an AGN) although even when an AGN is obviously
present it is still not apparent if reprocessed radiation from this source
dominates the submm emission. In contrast with the variation in the spectral
properties, we see relatively homogeneous morphologies for the population, with
a large fraction of merging or interacting systems. Our study shows that
virtually identical SEDs are seen for galaxies which exhibit strikingly
different opt/UV spectral-line characteristics. We conclude that standard
opt/UV spectral classifications are misleading when applied to distant, highly
obscured galaxies and that we must seek other means of determining the various
contributions to the overall energy budget of submm galaxies and hence to the
far-IR extragalactic background.
