"Part-time students, particularly mature undergraduates, seem to be an invisible and, in national policy terms, poorly understood cohort. "  This is Professor Sir Eric Thomas, introducing a recent UUK report on part-time HE.  The report makes grim reading, for the most part.  Over the past decade or so, whilst full-time undergraduates  have grown considerably (11%), the numbers of part-timers have shrunk, by about 17%. Much of my professional life has been spent promoting lifelong learning in one form or another, and especially part-time learning within universities, so this makes painful reading.  My last full-time job in the UK was with the country's oldest provider of such opportunities, Birkbeck, and I'm…