UTSL:

https://tfl.gov.uk/fares/how-to-pay-and-where-to-buy-tickets-and-oyster/pay-as-you-go/contactless-and-mobile-pay-as-you-go

"Contactless cards 

If your bank card shows the contactless payment symbol, you can use it to pay as you go straight away. You'll pay an adult rate fare.

Many contactless cards issued outside the UK can be used to pay as you go for travel (overseas transaction fees may apply):

• American Express (AMEX)
• MasterCard and Maestro (some cards issued in the USA, Canada and the Netherlands aren't accepted)
• Visa and V PAY (some cards issued outside the UK aren't accepted)

If you have a prepaid card, it may be accepted on our transport services. Check with your card issuer if you're not sure if your card is contactless or if it's rejected."

-seci