  The first observations to detect a population of distant galaxies directly in
the submillimetre waveband have recently been made using the new Submillimetre
Common-User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope
(JCMT). The results indicate that a large number of distant galaxies are
radiating strongly in this waveband. Here we discuss their significance for
source confusion in future millimetre/submillimetre-wave observations of both
distant galaxies and cosmic microwave background radiation (CMBR) anisotropies.
Earlier estimates of such confusion involved significant extrapolation of the
results of observations of galaxies at small redshifts; our new estimates do
not, as they are derived from direct observations of distant galaxies in the
submillimetre waveband. The results have important consequences for the design
and operation of existing and proposed millimetre/submillimetre-wave
telescopes: the Planck Surveyor mission will be confusion-limited at
frequencies greater than 350 GHz, even in the absence of galactic dust
emission; 1-sigma confusion noise of 0.44 mJy/beam is expected for the
JCMT/SCUBA at a wavelength of 850 microns; and the sub-arcsecond resolution of
large millimetre/submillimetre-wave interferometer arrays will be required in
order to execute very deep galaxy surveys. For the latest information see
astro-ph/9806063.
