I travel fairly often down to Paddock Wood from Bangor, and if I buy a through ticket the itinerary is invariably via London Bridge, whereas to my mind the more convenient cross-London connection is via Charing Cross. I have a couple of questions around this:
1. Is there a particular reason why this is so?
2. If I have an advance ticket, would I be able to use it from Charing Cross (assuming it is for a CX-origin train rather than a Cannnon Street one? I know it makes no difference on the tube, I have never failed to go through the barriers at CX.
3. Following from (2), does an advance restrict you to a particular southeastern service anyway? In the past it was just “required connecting service” but that seems to have changed now and my current ticket shows the LB connection.
Thanks
1) By default you will always be offered the itinerary the journey planner deems "fastest" that also complies with the route restriction. Depending on the exact timings of departures and the times set as the minimums for cross-London transfers, this could affect which London Terminal your journey is planned as using (where there is a choice of several).
2) You must follow your itinerary insofar as you are reserved onto a specific train - in your booking confirmation this will be shown by saying either the couch and seat you have a reservation for, or for some services it will say you have a reservation but no specific seat allocated. If your booking confirmation says that "reservations are not possible" on a part of your itinerary then obviously you don't have a reservation there. You'll find this is all reflected in the tickets you get when you pick it up at the machine - you only
must take those trains you have reservations for.
If there is a portion of your journey you don't have reservations for, you can take any unreservable service(s) such that you follow a permitted route. Whether or not a train is reservable will be indicated in the timetable at the station, or alternatively you can have a custom timetable created at
www.nationalrail.co.uk.
Sites such as
www.realtimetrains.co.uk,
www.opentraintimes.co.uk etc. will also tell you whether or not a given train is reservable. In general, many local services in the Southeast are non-reservable, though some are reservable. It's incredibly unlikely you'd get pulled up for using a reservable train you don't have a reservation for (on a local service), but in theory those are the rules.
So for your journey, as long as you were following a permitted route you would be able to take any non-reservable train from any appropriate London Terminal. Obviously you can't take the Mickey and wait around for 5 hours in London but there is definitely a level of flexibility if you travel a little earlier or later than your booking itinerary suggests.