  The ESA cornerstone mission The Far-Infrared and Submillimetre Sapce
Telescope (FIRST) has the ideal combination of sensitivity and angular
resolving power to determine the bright counts of galaxies over a large area of
sky in the submillimetre (submm) waveband. Important information about the
evolution of galaxies at moderate redshifts will be provided by the analysis of
these counts, and the effects of gravitational lensing will make the counts
even more significant for observational cosmology. This paper describes the
flux and surface densities of lensed galaxies in the submm waveband and
explains how FIRST could be used to discover several tens of lenses. The Planck
Surveyor and FIRST missions are very well suited to cooperate in this
programme, and together could compile a larger sample of several hundred
lenses. FIRST will be able to detect the signal due to the Sunyaev--Zel'dovich
effect in a large sample of clusters. These observations could also be used to
investigate submm-wave lensing by clusters, and to infer the properties of the
population of faint distant galaxies.
