Travelex ATM at LHR on 12/29:
Quoted exchange rate: 1.4434 USD/GBP
Quoted markup: 12.49%
Visa exchange rate: 1.283099 USD/GBP
Actual markup: 12.49%
It was easy enough to opt out, and it was interesting that the actual markup matched the quoted markup. Historically, the actual markup has typically been higher.