I live in SE, so to get anywhere by train you we have to go into London and out again.
If I buy a ticket from home to, say, Portsmouth, it will include the fare into London, my tube journey and the train out the other side. Am I allowed to chose my own route and/or get off the tube and continue my journey later in the day? Buying separate tickets for each leg works out much more expensive.
I've tried the website but can't find an answer, thought more experienced travelers might know?