Looking at fares from London to Brentwood and back on a Saturday, the cheapest fare I found on the Southeastern website was a super off peak day return at £8.30. The origin is down as London Terminals and all the trains shown depart from London Liverpool Street. If I amend the search to say avoid London Liverpool Street, I get the same £8.30 fare. However, the origins change to either London Bridge or London St Pancras. The itineraries for the London Bridge departures show travel by tube to Stratford and for London St Pancras show travel on HS1 to Stratford International and then "Metro" to Stratford. Being able to travel to and from London Bridge or London St Pancras with that ticket would be ideal, but I'm amazed that it seems to be possible. Is it really true?