  Substructures, expected in cold dark matter haloes, have been proposed to
explain the anomalous flux ratios in gravitational lenses. About 25% of lenses
in the Cosmic Lens All-Sky Survey (CLASS) appear to have luminous satellites
within ~ 5 kpc/h of the main lensing galaxies, which are usually at redshift z
~ 0.2-1. In this work we use the Millennium Simulation combined with galaxy
catalogues from semi-analytical techniques to study the predicted frequency of
such satellites in simulated haloes. The fraction of haloes that host bright
satellites within the (projected) central regions is similar for red and blue
hosts and is found to increase as a function of host halo mass and redshift.
Specifically, at z = 1, about 11% of galaxy-sized haloes (with masses between
10^{12} M_sun/h and 10^{13} M_sun/h) host bright satellite galaxies within a
projected radius of 5 kpc/h. This fraction increases to about 17% (25%) if we
consider bright (all) satellites of only group-sized haloes (with masses
between 10^{13} M_sun/h and 10^{14} M_sun/h). These results are roughly
consistent with the fraction (~ 25%) of CLASS lensing galaxies observed to host
luminous satellites. At z = 0, only ~ 3% of galaxy-sized haloes host bright
satellite galaxies. The fraction rises to ~ 6%, (10%) if we consider bright
(all) satellites of only group-sized haloes at z = 0. However, most of the
satellites found in the inner regions are `orphan' galaxies where the dark
matter haloes have been completely stripped. Thus the agreement crucially
depends on the true survival rate of these `orphan' galaxies. We also discuss
the effects of numerical resolution and cosmologies on our results.
