How to find your Nationwide IBAN online - taken direct from their site - had to do myself today so thought I would share...
International Bank Account Number (IBAN) EU use only Your IBAN number and the SWIFT address appears on your paper statement, directly above your list of detailed transactions.
If you are a registered Internet Banker you can view your statement history to obtain your IBAN number online (the BusinessInvestor account is not available online). To do this:
...select your account
...choose the 'History' tab, shown on the main part of the statement screen
...using the drop down menu select a date, then
...click on 'View statement'.
Your IBAN number along with your BIC and SWIFT intermediary bank address will be shown just above the statement details.
The following Nationwide Accounts have an International Bank Account Number (IBAN).
Account IBAN format
FlexAccount: GBxx NAIA 0701 16xxxxxxxx
CashBuilder Card and InvestDirect: GBxx NAIA 0700 30xxxxxxxx
BusinessInvestor: GBxx NAIA 0700 55xxxxxxxx
PortfolioInvestor: GBxx NAIA 0700 66xxxxxxxx
Nationwide's SWIFT address is: NAIAGB21 (This number is also known as our BIC - Bank Identifier Code). You will also need to quote the SWIFT Intermediary Bank MIDLGB22. This is for all Nationwide accounts.