I was always under the assumption that contactless transactions were an almost failproof method of stopping DCC. But I'm not sure now.

Previously, all my contactless transactions have been autorised 'offline'. Auth codes from my bank are digits only when offline and they don't affect my 'available balance' until the payment is processed a few days later. Transactions are written to the transaction log held within the card's chip (there is an Android app to read this from the card).

Today, however, I used my credit card contactlessly at a petrol station in Cambridge (UK). The transaction was authorised online as the auth code started with a letter (convention my bank follows) and (importantly) it was not written to the transaction log within the card's chip. It struck me that it would theoretically be possible (if my card was not in GBP) to have been DCCed *after* touching the card but before receiving the receipt and without needing for the card to be retouched on the reader.

Anyone with any experience of contactless DCC?