Back to the OP, I've found www.trailwise.org.uk
to have a good database covering all of the UK. Quality varies from county to county as it depends upon user input to stay up to date with TROs and changes in local conditions. You'll need to belong to TRF or another participating group to have access to all details. I'm loading up promising routes in Essex, Herts, Suffolk, and Cambridge, checking them against on-line Definitive Maps of the County Councils, then checking the regional discussions on the TRF forum, then riding out to see what I find, then sharing that knowledge backon Trailwise. That's the plan, anyway.