In message , at 15:18:33 on Thu, 21 Nov
2013, Mizter T remarked:
TfL hasn't actually got a policy of not accepting foreign issued CPCs
on buses, rather they just promote the scheme as accepting UK-issued
contactless credit/debit/charge cards because they can't guarantee
foreign issued ones will work.

See this PDF from TfL - "Using contactless payment cards
on buses":
http://www.tfl.gov.uk/assets/downloads/tickets/Using_contactless_payment_cards_on_buses.pdf

---quote---
Most contactless payment cards (CPCs) issued by UK banks and payment
card companies will be accepted on buses but some cards issued outside
the UK will not.
---/quote---

But my understanding is that they are refusing some foreign/prepay cards
because of problems in the back-office processing, rather than because
there's a technical issue with the cards themselves.
--
Roland Perry