(posted 8701 days ago)You do not have to explain why you are serving the subject access rights order on them (unless the Data Protection Act now contains a clause that I hadn't noticed).
You are exercising a legal right that you already have, and you are exercising it to try to resolve the Nationwide's claim without either of you having to bother the courts by taking your dispute there.
So I suggest you send a copy of their letter to the Data Protection Registrar (see its site at http://www.dpr.gov.uk for details.) and ask the DPR to investigate (They will send you a complaint form to fill out.)
In the meantime, write to the Nationwide politely pointing out that they have 40 days to comply with your request and that you await their response to your original request. There's no particular need to threaten them with a complaint to the DPR - no lender is frightened of the DPR but you should make sure your letter says that you are using the DPA to try to resolve the Nationwide's claim without either of you having to bother the courts.
You may find that the DPR is unwilling to upset your lender but any letters you have that show the Nationwide was unwilling to comply with Data Protection law or was obstructive to your attempts to sort the issue out when you tried to use the law to resolve their claim without having to go to court - will make them look like oafs in front of a judge.
Judges hate plaintiffs who have obstructed the other party's attempts to resolve the issue out of court and can award costs against them. This will likely reduce Nationwide's willingness to actually go to court over your claim - despite what their letters might say.
You clearly have concerns about the Nationwide's numbers so you are absolutely right to seek more information - you don't have to tell them exactly what your concerns are. You only need to say that you are seeking information in order to deal with their claim as quickly as possible.
In short, the more resistance Nationwide puts up to your attempts to resolve the claim outside of the court, and the more it does it in writing, the better for you.
Incidentally, lenders routinely submit high sales agent costs as part of shortfall claims but 8% is among the highest I have yet seen. You have every reason to be concerned and to seek more information.
I would also love to have copies of the Nationwide's letters to you.
Lee