The larger central number is the main sheet: if present, the letters A-P indicate that the Sudan Survey produced a map of that area.
Click on the sheet required to view which (if any) sheets are held by Durham University Library.
This will take you to our catalogue: where digitised copies of maps are available, a link "View online" will be present. Click on this to launch the viewer. This viewer requires a plugin to be installed, instructions for doing this will appear if you do not yet have the viewer on your computer.