I take it that's the Rylands Bagshaw stuff you're wanting to look at? I thought that collection was publicly accessible, I know some of my PDMHS colleagues have been up to look at stuff in recent years and I don't recall any mention of having to jump through hoops to get access. If you do need a reference though, I'd suggest your club secretary does a quick letter explaining who you are and what your interest in the relevant documents is, that ought to be sufficient.
Phil - much as I'd love to have a trawl through the Putterell stuff, as usual I'm lacking the time and my current priority is to get the Field Grove and Senior map articles finished off and handed over to Richard Shaw! It will need a quick trip to the archives though, just noticed that there are copies of some of the Welbeck Senior maps in the Bagshaw collection....