Sup.
Sandy Lane is a bit of a mining hotspot. Although there are several modern-ish abandonment plans and quite good mining-area-maps, the picture is by no means complete. There is a fair bit of shallow and ancient stuff around there. The lego estate opposite your plot dug up lots of shallow features. You'd have to chase the people who did the original site work to see whether any of these were likely to continue under your plot and what form they took. There is no substitute for digging it up, or poking it with a drill. The area maps are pretty good, but since they are large scale and a bit of a "indicator" rather than a spatially accurate plan, the person making the judgement needs to take this into account.
All old maps and plans are not created equally. Some of the distances measured are "3 chains, as far as I can spit and half a dogs tail long"
The field is probably OK for putting chickens on, if a developer was to develop it, they'd almost certainly recommend having a dig. If you were developing it yourself, you'd be foolish not to.
There is nothing in law stopping you from sinking all your money into a dream home sited right on top of a massive hole.
After all, this isn't about chickens, eh? :lol:
If you're going to develop it, get a proper firm backed up by proper insurance to do the job properly. If you don't, you'd be betting that it's fine.....which of course it PROBABLY is.