Or, if you want to do things off your own back. Buy OS maps of the area you want to use and take them into the local Highways Department, they should help you to mark up your maps from the Definitive Map. Notts Highways used to be quite good at helping mark maps, but staff do change and know that Lincs Highways staff are no where near as pleasant.
Onto the Soapbox now;
Please make sure your vehicles are taxed, tested and insured and that the riders / drivers hold a licence to drive the vehicle they are in control of. I have met, and had very heated discussions with far too many people using lanes for kids quads / pitbikes and adults on motocrosser
Also please be respectful of other users you meet, even if they do not reciprocate. Keep your speed down, I meet far too many motorcycles using the lanes travelling at mach 2
And finally, if you find a lane is getting badly cut up and too muddy, stop using it!!! Or you could find the council closing it. If you do meet 4x4's 'Mud Plugging' challenge them, take their car numbers, any good GLASS or LARA area rep will kick their arse if they are members. The club I'm in will not use bad lanes for months to give them time to recover.
Contact other user groups and tell them about its condition too. Join GLASS and help on one of the national green lane repair days, if only to give you the moral high ground when challenged by irate Ramblers.
The lanes are there for everyone to enjoy, not for a few to destroy.
Keep the wheels muddy and turning