This is the full list, correct as of September 2010:
Network Rail:
31105 (NR yellow - Active)
31233 (NR yellow - Active)
31285 (NR yellow - Active)
31465 (NR yellow - Active)
British American Railway Services/DCR:
31422 (Intercity standard - Stored)
31452 (DCR green - Active)
31454 (Intercity swallow - Active)
31468 (Fragonset - Out of traffic pending overhaul)
31601 (DCR green - Active)
Rail Vehicle Engineering Ltd:
31106 (BR blue - Active)
31459 (FM Rail debranded black - Active)
Hanson Traction:
31190 (BR green - Out of service, but no longer used on test trains anyway)
31602 (NR debranded yellow - On long term hire to NR)