So my question is, when I renew my SWT▸ season ticket next year can I give up using the tube by having a ticket to "London Terminals"? Can I get off my SWT train, leave the barriers at Waterloo, walk to Waterloo East and catch a South Eastern train to London Bridge using this ticket?
Yes most definitely. 'London Terminals' for a ticket from Bookham, and most areas southwest of London, is quite flexible, and as well as Waterloo, includes Victoria, Charing Cross, London Bridge, and less obviously Cannon St, Blackfriars and City Thameslink (but no further).
Historically these stations correspond to a ticketing group formerly known as 'London
SR▸ '. The ticket barriers at Waterloo are programmed to pass tickets through to allow this onward travel.
Paul