After searching for right-of-way access for my off-road cycling, I chanced upon this website. What a great resource!
Anyway, back to the matters in hand. The following pic (grid ref: SU6648), shows the start of Longroden Lane. Did you actually manage to traverse the entire lane until it reaches the Tunworth/Basingstoke road, opposite Huish Lane? The 'lane' seems to disappear into fields, heading into private land.
SU6648 : Tunworth