For the TouchPay trial, NatWest is sending customers a free iCarte case that provides two-way NFC communications from an iPhone 4s and iPhone 4 to Visa PayWave terminals.

Once attached, customers are prompted to download a TocuhPay app from the bank, which must be launched in order to make a transaction. Users may configure the phone to operate like a contactless debit or credit card, requiring only a touch of the reader at the POS terminal to make a transaction. Alternatively, they can elect to enter a passcode for each individual purchase of £20 or less.

Australia's Commonwealth Bank offers the iCarte option for iPhone users as part of its Kaching mobile banking service. Available as a standalone free application, Kaching allows users to send money to others, either via text message, email or through Facebook. Users wishing to make payments at contactless terminals can buy the iCarte case for £54.95 from within the app.

In a statement on its Website inviting customers to sign up the services, NatWest says: "This is a trial of a new service and therefore is only available for users of iPhone 4S and iPhone 4 at this time. We hope to make TouchPay available for other smart phones in the future."