Bumped into the officer in charge of health and safety in the area a couple of months ago, he was out showing around some la de das who ran the wildlife trust in the area, well something like that.
Got in a really good conversation with them, my understanding from the conversation is the crux of it is that they have to be seen to be actively showing due diligence on the health and safety front for all users, public liability and all that. IE if a public user gets hurt on the land and the army has not demonstrated due diligence, they are liable. A way they demonstrate this is to enforce the bye law stopping public users going anywhere other than the public rights of way. Though his words were, by informing us of the use restrictions, to not continue riding on anything other than public right of way, he was showing due diligence.
I ride the MOD land 4 times a week, this was the only instance where i've had a talking to from someone, it just so happened to be the bloke in charge of it, he was very well prepared, very polite and a pleasure to talk to.
My gut instinct from the conversation was as long as use of the land is well respected, turn around when see an exercise, cut out the night riding, nothing bad will come from it, enforcing the bye-law is there to give their warning some clout, but at the end of the day my understanding is that worst case is prosecution for a £500 fine, for me, not the end of the world considering the lifetime of riding i've had on the land.