  LOFAR, the Low-Frequency Array, is a next-generation software-driven radio
telescope operating between 30 and 240MHz, currently under construction by
ASTRON in the Netherlands. This low frequency radio band is one of the few
largely unexplored regions of the electromagnetic spectrum. The sensitivity and
angular resolution offered by LOFAR will be two to three orders of magnitude
better than existing telescopes, and as such it will open up this new window on
the Universe. LOFAR will impact on a broad range of astrophysics, from
cosmology to solar system studies.
  There is growing European involvement in LOFAR, driven by the need to add
stations far from the main core in order to improve angular resolution.
LOFAR-UK is a project aimed at cementing UK participation in LOFAR via the
operation of four stations within the UK. LOFAR-UK ground stations will allow
LOFAR observations to reach sub-arcsecond scales at the highest frequencies,
and as a result will also improve the (confusion-limited) sensitivity limit of
the telescope for deep surveys.
  LOFAR-UK will achieve involvement for UK astronomers in a world-leading
science facility operating in the immediate future. It will allow the UK to
build up important scientific and technical expertise in `next generation'
radio astronomy in preparation for the Square Kilometre Array (SKA), and will
play an important role in broadening the UK community that has an interest in
radio astronomy. This White Paper outlines the strategic importance to the UK
astronomy community of gaining involvement in the LOFAR project, the scientific
interests of UK researchers in using the telescope, and the technical
challenges that will need to be overcome [abridged].
