If there’s not one already, seriously consider organising a local club affiliated to British cycling as a first step, if nothing else it lends a bit of legitimacy to MTBers in the area as an organised, serious group.
Further down the line when issues such as liability insurance and trail maintenance are brought up (and they will be) there is a representative body for MTBers and the British Cycling connection can help with advice in these areas too…
Maybe try getting in touch with those at existing successful clubs, I used to Ride regularly at Chicksands myself, whatever your feelings about it as a venue that would never have developed and seen such extensive, well maintained trail building and event organisation without a strong well organised club, Swinley is another good example of a strong local Club contributing to the success of a woodland as a venue for cycling, Aston hill too, there are loads really, just remember there is some strength in numbers, push the “Local Tourism” angle if you can and be prepared to negotiate rather than argue…