  We present a new version of the GALFORM semi-analytical model of galaxy
formation. This brings together several previous developments of GALFORM into a
single unified model, including a different initial mass function (IMF) in
quiescent star formation and in starbursts, feedback from active galactic
nuclei supressing gas cooling in massive halos, and a new empirical star
formation law in galaxy disks based on their molecular gas content. In
addition, we have updated the cosmology, introduced a more accurate treatment
of dynamical friction acting on satellite galaxies, and updated the stellar
population model. The new model is able to simultaneously explain both the
observed evolution of the K-band luminosity function and stellar mass function,
and the number counts and redshift distribution of sub-mm galaxies selected at
850 mu. This was not previously achieved by a single physical model within the
LambdaCDM framework, but requires having an IMF in starbursts that is somewhat
top-heavy. The new model is tested against a wide variety of observational data
covering wavelengths from the far-UV to sub-mm, and redshifts from z=0 to z=6,
and is found to be generally successful. These observations include the optical
and near-IR luminosity functions, HI mass function, fraction of early type
galaxies, Tully-Fisher, metallicity-luminosity and size-luminosity relations at
z=0, as well as far-IR number counts, and far-UV luminosity functions at z ~
3-6. [abridged]
