The only “rool” you need to know is that the only remedy in law for riding a bike somewhere that isnt a bridleway is through damages.
How much damage an MTB tyre does compared to a walkers foot is one for a Saturday pub debate. But damages are a relation of losses. So…… as long as you make sure whatever you do doesn’t create a substantial loss (riding through a poult pen 2 weeks before the beginning of the shooting season and scaring them all away, say) I reckon the quick offer of 50p to cover the “damage” of a cycle track (paid “in to court” 🙂 ) will suffice. And even then, you need the landowner or the agent to catch you*.
Quite simply, if you’re not being a douche, there’s no real reason why you cant ride any reasonable path. That’s my tenet and Im sticking to it.
* doesnt work with by-laws though.