MSSL is involved in several aspects of XMM-Newton, in particular the Optical Monitor (OM) and the Remote Grating Spectrometer (RGS). Please see the XMM-Newton, OM and RGS for further information on the instrumentation and projects.
Data from the OM have been used to create a catalogue of Optical and UV sources. This has been updated with a second version in 2014. For information see XMM-SUSS2.