Anyone else can correct if I'm wrong, metro routes a lot are DOO with the exception of the following stations:
London Bridge
London Victoria
East Croydon
Purley
Three Bridges
Redhill
Brighton
Gatwick Airport
Clapham Junction
Balham
Haywards heath
The Uckield, east grinstead and Milton Keynes central lines have conductors on board
Hope this helps, I'm going off of memory and my local lin