  A radio-based search for strong gravitational lensing, with image separations
in the range 160-300 milliarcsec (mas), has yielded a null result for a sample
of 1665 sources (Augusto, Wilkinson & Browne 1998) whose mean redshift is
estimated to be ~1.3. The lensing rate for this previously-unexplored
separation range, <1:555 at the 95% confidence level, is less than on
arcsecond-scales - as expected from models of lensing galaxy populations.
Lensing on 160-300 mas scales is expected to arise predominantly from spiral
galaxies at a rate dependent on the disk-halo mass ratio and the evolving
number density of the population with redshift. While the present sample is too
small for there to be a high probability of finding spiral galaxy lenses, our
work is a pilot survey for a much larger search based on the full CLASS
database which would provide useful information on galactic structure at z~0.5.
We examine other possible lens populations relevant to our present search, in
particular dwarf galaxies and supermassive black holes in galactic nuclei, and
conclude that none of them are likely to be detected. Our null result enables
us formally to rule out a cosmologically significant population of
uniformly-distributed compact objects: Omega (CO)<0.1 (95% confidence) in the
mass range 10^(9.5) - 10^(10.9) Mo.
