In future I intend to do more OS map research. The other day I went up to the Ridgeway - heading down a track through farmland, but after ~200m was confronted with something like 'Private Road. Persons using will be liable to prosecution'. So I U-turned, and when down elsewhere. I've since consulted OS map, and it is a restricted byway, so would have been fine on my bike (being human, rather than 'mechanically' propelled).
Re. the 'Yatton Weston sluice track', still tempting to use it to avoid 4km of the busy A370 (Congresbury to M5 Weston jnct). However it was only exploring a possible route via Cheddar then Strawberry line to Yatton, to do with a Weston friend.