When Waterloo has had major delays recently there have sometimes been many empty trains at platforms but out of service due to no drivers being available. How did they get there?
Oh, so have SWR given up on "full crew workings" again where the driver, guard and stock stay together for as long as possible? It was given up by Stagecoach early in their franchise to cut costs and reinstated about 5 years later to improve reliability and reduce delay attribution costs.
(Basically start of shift to break and then normally with different stock to the end of the shift.)