martyn dawe wrote:

I thought a uncompleted journey only kicked in if you failed to pass
your oyster card thro a reader at the end of the journey(or reader
error) ?

I believe there is a time out, otherwise people could nip through the
barrierless exits, do their business and then pop back in and touch out at a
much cheaper point on the system.

I think it's two hours which is supposed to cover all journeys on the
system - but does that include the likely waiting time on platforms? What
happens if you touch in at Chesham only to see the train doors close, and
then thanks to delays don't get onto the main part of the Met for nearly an
hour?