As of the 16 March 2015 Nationwide no longer offer this service.

If you're registered for Internet Banking you can make a SWIFT payment online from your current account or in branch. It’s a fast, secure way to transfer money between countries.

Cancelling a foreign draft

If you decide not to use the draft, you should return it to your branch for cancellation. If the draft was drawn in a foreign currency, it will be converted back into sterling at the exchange rate on the day it is cancelled. The balance will be credited to your account but may be less than you originally requested as a result of exchange rate movements.
If the draft has been lost or stolen, you should let your branch know immediately and they will arrange for it to be stopped. You will be required to sign an indemnity covering Nationwide in the event that the original beneficiary presents the draft for payment.