I find that many of the Sustrans routes are quite convoluted, goig to great lengths to avoid main roads or towns and have things like chicane barriers quite often.
The nice thing about biking in England is the huge network of small country lanes. Most of the cars stick to the A-roads and leave these B-roads and unclassifieds alone. I agree with Raybo that the best option is a 3 miles - 1 inch atlas with the pages ripped out. There's rarely any need to spend out on an OS map.