I have 2 family members that were both train drivers, one for Southern and one for South Eastern. They did the same job but the differences in their expected working practices were amazing. For one Sunday was a normal working day whilst the other worked Sundays on a voluntary basis and got paid a premium.
South Eastern have run their trains driver only for years unless the train goes further out of London than Sevenoaks. This was negotiated by the Union and the operating company and has worked well ever since.
Southern is owned by Govia — a joint venture between transport groups Go-Ahead Group and Keolis (a SNCF subsidiary) — which also owns the neighbouring Southeastern.