We moved house recently. Changing the address for credit cards just involved a phone call. The bank accounts however needed the change in writing so we duly went into the branches and correctly filled in the forms.
The first statement from Nationwide was addressed to us in Hull, Suffolk. I phoned up the call centre (not a foreign one if the girl's Scottish accent is anything to go by) and I was asked "...and is that wrong?". She said she was unable to correct the bank's mistake on the phone, insisting that we should call in to the branch.
On the whole we've been fairly happy with Nationwide until now.