The BHS have "Bridleway Access Officers" all over the country. How effective they are I do not know but a call to the BHS will establish who your's is. That is not to say that the bridleway wil be usable but it is a start.
Good luck. Also look on your local Ordnance Survey map. Bridleways are marked with long dashed green lines, as oppose to footpaths which are short dashes.