Hiya if you go to the following website and register ( which is free if I remember correctly?) they have loads of information about bridleways and I think they include distances too? ( not entirely sure as it was ages ago when I went on there to have a look) http://www.bridleways.co.uk/
It's brill! I found some pre planned routes. I was wondering, is there a function where you can map out your own route or is do you do that and add it on the database?