Matthew wrote:
.. .
The gates at London Bridge on the National Rail platforms will let
you
through with only prepay on an oystercard, but will not deduct any
fare or resolve the journey. The validators on platforms 5/6 must
be
used even if you have already touched in or out there.

That could be useful to know, if only to avoid putting my season
ticket
through the gates.

Frequent use may well be monitored to stop "dumb-belling".

What does 'dumb-belling' mean?

Does anyone know the position with the gates/validators at
Farringdon? A
typical scenario is an occasional journey Brighton to Moorgate and
return:

1. I use my National Rail season which is valid as far as City
Thameslink.

You are travelling without a valid ticket between City Thameslink and
Farringdon. To combine a paper National Rail ticket and Oyster Prepay
you must touch in where your paper ticket ends, at City Thameslink.

2. At Farringdon I validate the prepay card on the platform (does it
matter
which platform I do this on?) and then
3. Change to the Underground for Moorgate.
4. At Moorgate I the prepay card lets me out through the gates.

Prepay requires a touch in and out, so your usual journey is valid
between Farringdon & Moorgate. Just touching out at Farringdon would
lead to an unresolved journey.

Fascinating. So you'd have to get out at CT, go up to the ticket hall
to touch in, then come back down again and get on another train for the
10 second journey to Farringdon?

In that case I suppose the Farringdon validators are actually intended
for people changing *onto* Thameslink, having used Prepay to get them
there on the Tube (since otherwise you would be leaving the Tube
without passing through a gateline). In fact I can't think of any way
they could be used in the opposite direction (though I suppose someone
might *theoretically* have e.g. a Brighton - Farringdon LU season...)

In a way it's a shame, because the type of journey the OP mentioned
would be extremely useful for me (given that Tube interchange at
Elephant & Castle is such a faff!) Perhaps they should install
validators on the trains...

On a related note, has anyone ever tried using Prepay on the Kentish
Town - E&C section of Thameslink? If so, were you charged Tube fares
for doing so?