Ordnance Survey Maps are one of the great things given to us by the Victorians. At the 1:25,000 and 1:50,000 scale they are excellent maps. If you have the money you will need numbers 155, 154, 169, 168 and
167 to cover the main route, plus 143 to include Ely. Generally these cost less than £6 each.
Working in scales coarser than this means using Philips. (The usual alternative, Harvey, do not publish a map for this area.) Philips have a wide range of maps, including their Atlas range.