  UW CrB (MS1603+2600) is a peculiar short period X-ray binary that exhibits
extraordinary optical behaviour. The optical light curve shape of the system
changes drastically from night to night, without any changes in overall
brightness. Here we report X-ray observations of UW CrB obtained with {\it
XMM-Newton}. We find evidence for several X-ray bursts confirming a neutron
star primary. This considerably strengthens the case that UW CrB is an
Accretion Disc Corona (ADC) system located at a distance of at least 5--7 kpc,
  (3--5 kpc above the galactic plane). The X-ray and optical monitor
(UV+optical) light curves show remarkable shape variation from one observing
run to another, which we suggest are due to large scale variations in the
accretion disc shape resulting from a warp which periodically obscures the
optical and soft X-ray emission. This is also supported by the changes in
phase-resolved X-ray spectra.
