  We investigate the number counts, clustering, morphology and radio/X-ray
emission of extremely red objects (EROs), defined as galaxies with R-K>5.0.
This criterion will select old, passive ellipticals at z>0.9. To K=21 we
identify a total of 158 EROs in 81.5 sq. arcmin. The ERO number counts are
lower than predicted by a pure luminosity evolution model, but higher than
predicted by current CDM-based hierarchical models. They can be fitted by a
combination of moderate merging with a decrease with redshift in the comoving
number density of passive galaxies. We investigate the angular correlation
function and find that the EROs have a much higher correlation amplitude than
full K-limited samples of galaxies. This implies that the intrinsic clustering
of EROs is stronger than that of present-day E/S0 galaxies. We estimate the
comoving correlation radius as 10-13 Mpc. We estimate seeing-corrected angular
sizes and morphological types for a K<19.5 subsample (31 galaxies), and find a
3:2 mixture of bulge and disk profiles. 1/4 appear to be interacting, disturbed
or irregular. The angular sizes of the bulge-profile EROs are consistent with
passively evolving ellipticals at 0.9<z<2. Seven of the bright EROs are
detected as 1.4 GHz radio sources. The strongest, at 5 mJy, is also a Chandra
X-ray detection, and lies at the centre of a possible cluster of EROs. Another
source is elongated and aligned with the optical axis and may be a ULIRG-type
starburst.
