Thanks very much for this fast and helpful answer!

On Tue, 23 Oct 2007 16:08:25 -0700, Mr Thant wrote:

if I were travelling in the daytime then
presumably I could get off the loop train at Greenwich and get back on
it subsequently to go home.
Yes.

Good to know.

No. Following the Routeing Guide rules, the only permitted route is
direct via Lewisham and Sidcup (the shortest route), or via a direct
train.

That's interesting. I think on at least one occasion when there's been
rail works I've probably technically breached this - I needed to get my
bike into London, which wasn't going to happen on a rail replacement
bus, so I went down to Dartford and back up a different line to London,
on an all zones travelcard, which of course doesn't cover Dartford (one
of the sillier bits of drawing up of the zones IMHO but I'm sure there
were reasons for it! I'd always assumed this was due to Dartford being
outside Greater London but then I realised recently that in various
other areas Zone 6 extends into neighbouring counties). Hopefully
they'd've been understanding in the circumstances.

Indeed, at times of the week when train services are less frequent, it's
not uncommon for National Rail Enquiries to suggest travelling away from
London and changing at Dartford among its options for getting to London
from Crayford. Does this mean it is a 'valid route' for a Cheap Day
Return?
The journey planner has no official authority to permit a non-
permitted route. Does the red "you need to buy two tickets" warning
appear?

I haven't noticed it in the past but I've just searched now with a
forced 'via Dartford' option and it does indeed give that warning.

If so, does that mean I can travel to, and break my journey at, Greenwich?
Not unless the train you get off and then on at Greenwich was London-
Crayford, no.

I see. The upshot of this is that the loop line is even more of a useful
service than I'd realised! Shame they don't operate it outside that
narrow daytime period.

As a final twist, if you do break your journey at a particular station,
are you then obliged to resume your journey at that same station?
No, but it has to be further along a particular permitted route that
covers both legs. Switching from Lewisham to Greenwich wouldn't be
allowed.

Makes sense. This whole system is far more logical than I'd hoped

(I'm assuming you want to follow the rules strictly. What the rules
say and what you can get away with are very different things)

For the sake of a couple of 90p buses or whatever, I might as well play
by the rules. I wonder how the possible future change to zonal ticketing
(as opposed to zonal fares as at present) will affect all this - perhaps
they'll just kill off the concept of break of journey, since no such
thing can presumably exist in an Oyster PAYG context where you're
charged for leaving the system.

Thanks again for your help,

Paul