I agree on the state of it! I went through there on a bicycle in the summer (S->N). I recall it being signposted as a footpath from the northern end so I'm intending to head back out there at some point before checking with the council.

I'm not sure of the best way to record this in OSM, though.

- "designation: unclassified_highway" makes sense; it's not a documented tag as far as I can see, but none of the others fit.

- "highway: footway" makes sense as a physical description of (most of) the track. Perhaps the southern section should be "highway: track".

I'd like to add "bicycle: yes" to both parts, but perhaps with a suitable surface quality tag, and a break as it crosses the A11. Is that reasonable? There's often a tension between what's legally allowed and what's actually a good idea.

For what it's worth, I noticed this only because cycle.travel's rendering shows it as a (rough) cyclable track, but OSM doesn't. I thought you'd changed it, but it appears not.