The Darkness II, PC – £3.09
The Darkness II, PC – £3.09
Registers on Steam.
To purchase digital games from Amazon US, use your UK Amazon account, and add a US billing address to your account. This address needs to be a valid US address, but nothing will be sent there, and you can access all your games through their website. Some card issuers may charge a fee.

http://www.which.co.uk/money/bank-accounts/reviews-ns/bank-accounts/charges-to-use-your-debit-card-abroad/ this chart matches what Natwest have charged me for using my debit card so should give a good idea for others too
Cheers for that Chris.