There were mixed passenger/parcels trains on the WR Thames Valley services using a 128 DPU running in multiple with a 117 set. The 128 shuttled back and forth on it's own between Paddington and Reading during the day, but ran combined with passenger DMUs in the peak, presumably to save a train path.
Not sure of the exact working, but it ran into the sector era in the late 80s with the 128 in Royal Mail livery and the 117 in NSE. Think the practice of a parcels van as tail traffic had ended long before then,