Also, many of the U.K. area frequencies have 2 ATCOs on them, called Radar/Co-ordinator, or Tactical/Planner. It is usually the Radar/Tactical's voice that you hear, but the Co-ordinaor/Planner, occasionally transmits messages.
For occasionally, read never, especially in London en-route. I don't know if they do at Scottish and I know they do it in Ireland, but not for London