Originally Posted by
WHBM
Besides which, it's a very profitable arrangement for London Transport. If you don't manage to touch in, but then change onto the Underground at Canning Town (like our OP Swiss Tony did), and then have to touch out in Central London, you automatically get fined what, £5 now, on your Oyster card, for an "incomplete journey".
FWIW, the gate at Canning Town deducted £4.60 from my card (I checked). I then had another £2 plus some p deducted when I exited the station in zone 1.