Some of it is TRO’d from memory. Otherwise, not much near Gloucester. There’s a short section near Shurdington, and one or two lanes in the Cotswolds.
Salisbury Plain is around an hour away, we’ll worth a drive. There are groups on FB who go regularly. Otherwise, there’s some good lanes in North Somerset and just south of Bristol, less than an hour away.
The only local club is Cheltenham and Cotswold LRC. I was a member some years ago but due to other commitments, I’m not now. They do the occasional greenlaning trips, a few times a year.