A Google of the post code reveals quite a few links, many on Barclays/Woolwich site.
When I looked at the PO Box address it says "Leicester" I expected we were looking for a 0116 (Leicester) number. However,
this leaflet list fax numbers of 01322 428 071/428 077 below it.
Search the database for
woolwich. There are a few 01322 numbers listed for mortgage enquiries.
Let us know how you get on as it may help others with the same query.