I'm based in Herts and we seem to be poorly off for Green Lanes.
I have recently joined GLASS and have access to their rather antiquated, yet apparently up to date, list of green lanes. There are some around Bovingdon and more further North.
I am hopefully going to get out in the next few weeks and try a few lanes for the first time. Whereabouts are you in Herts?
Gimme a PM and we can maybe arrange something.
Rgds,