thank you for your response. We actually arranged the mortgage through the mortgage shop back in April/May (who had their own set of faults), but for providing this document, we dealt directly with Skipton, but I can't remember who with. We sent a scanned copy of a document proving the source of funds, which was missed, meaning that we were asked again for proof. After trying to find alternative proof, we resent the document, which it turned out was sufficient. We also ended up having to provide additional bank statements to bring the application up to date because of the initial delay between us submitting the application and it being processed. However we don't know whether the delay was with the mortgage shop or Skipton.
In the grand scheme of things, these were minor annoyances and Skipton did indeed sort out our mortgage, but they were things we probably could have done without when going through the stressful process of buying a house.