I haven't the time - or resources - to explore this fully, but there does seems to be plenty to find about a nexus of Marxists and revolutionary socialists at St Catherine's College, Oxford, starting as early as the 70s* and forming the background for Peter Mandelson and others with connexions to New Labour. I should be grateful for more insights.
*With much deeper roots - e.g. Terry Eagleton was a protege of Raymond Williams.