Using the Prime Focus CCD Camera at the Isaac Newton Telescope we have determined the form of the B and R galaxy number-magnitude count relations in 12 independent fields for 21m < B(ccd) < 25m and 19m < R(ccd) < 23m.5. The average galaxy count relations lie in the middle of the wide range previously encompassed by photographic data. In our independent data set, we find reasonable agreement with the CCD galaxy counts of Tyson at these depths. Further, the field-to-field variation of the counts is small enough to define the faint (B < 24m.5) galaxy count to +/- 10 per cent and this variation is consistent with that expected from galaxy clustering considerations. Our new data confirm that the B, and also the R, galaxy counts show evidence for strong galaxy luminosity evolution, and that the majority of the evolving galaxies are of moderately blue colour (0 < B-R < 1.4). We discuss this result in the light of current theories of galaxy evolution. We conclude that simple models of the type described by Bruzual may explain both our n(B) data and the n(z) data available in faint galaxy redshift surveys, at least if an intermediate value for the uncertain bright count normalization is assumed. Thus we believe that there is no need yet to invoke a more complicated luminosity dependent evolution of the type suggested by Broadhurst et al. However, more R evolution is required to fit the n(R) and n(B-R) data than is predicted by a simplified version of the Bruzual models. Finally, we have used our counts to make a new test of the tired light cosmological model.
