Was testting a Beta version of a new Android app for caching, Cachehound, and saw that it had RMaps as it's mapping. One of the abilities of RMaps is to be able to use User Defined Maps and to add Custom Maps to to this list.
I now have a 1:25000 OS maps that I can use off line along with all my PQ files that I have loaded.
The attached PDF explains where to get the software and how to create the mas.