  We have carried out surface photometry and an isophotal analysis for a sample
of 25 early-type dwarf (dE and dS0) galaxies in the Virgo cluster based on CCD
images taken at the VLT with FORS1 and FORS2. For each galaxy we present $B$
and $R$-band surface brightness profiles, as well as the radial colour ($B-R$)
profile. We give total apparent $BR$ magnitudes, effective radii, effective
surface brightnesses and total colour indices. The light profiles have been
fitted with S\'ersic models and the corresponding parameters are compared to
the ones for other classes of objects. The observed profiles of the brightest
cluster dwarfs show significant deviations from a simple S\'ersic model,
indicating that there is more inner structure than just a nucleus. In addition,
we find a relation between the effective surface brightness, at a given
luminosity, and the strength of the offset of the galaxy's nucleus with respect
to the center of the isophotes. Dwarfs with large nuclear offsets also tend to
have stronger isophotal twists. In sum, our findings suggest the presence of
substructure in most, and preferentially in the less compact, bright early-type
dwarfs. The physical (dynamical) meaning of this has yet to be explored.
(abridged)
