The Iban type exposes several convenience properties to extract components of an IBAN.

IbanParser parser = new IbanParser(new IbanValidator());
Iban iban = parser.Parse("GB29NWBK60161331926819");

Console.WriteLine(iban.Country.TwoLetterISORegionName);  // GB
Console.WriteLine(iban.Bban);                            // NWBK60161331926819
Console.WriteLine(iban.BankIdentifier);                  // NWBK
Console.WriteLine(iban.BranchIdentifier);                // 601613

Note that BankIdentifier and BranchIdentifier are not supported for all countries and registry providers, in which case null will be returned. Either identifier is guaranteed not null when the country specification defines positional information, which can can be looked up in the IIbanRegistry.

You can also access a country its registry information via the iban.Country property, for example: iban.Country.Branch.Position.