  We consider homogeneous crystallisation rates in confocal microscopy
experiments on colloidal nearly hard spheres at the single particle level.
These we compare with Brownian dynamics simuations by carefully modelling the
softness in the interactions with a Yukawa potential, which takes account of
the electrostatic charges present in the experimental system. Both structure
and dynamics of the colloidal fluid are very well matched between experiment
and simulation, so we have confidence that the system simulated is close to
that in the experiment. In the regimes we can access, we find reasonable
agreement in crystallisation rates between experiment and simulations, noting
that the larger system size in experiments enables the formation of critical
nuclei and hence crystallisation at lower supersaturations than the
simulations. We further examine the structure of the metastable fluid with a
novel structural analysis, the topological cluster classification. We find that
at densities where the hard sphere fluid becomes metastable, the dominant
structure is a cluster of m=10 particles with five-fold symmetry. At a particle
level, we find three regimes for the crystallisation process: metastable fluid
(dominated by m=10 clusters), crystal and a transition region of frequent
hopping between crystal-like environments and other (m\neq10) structures
