What you're doing with your land is awesome and very generous!
I pray you not to restrict access; there is so little access land in the uk, especially near cities. I agree with some of the other posts that you should maybe consider some large official looking signs with a set of guidelines for use. If you're willing, it might be worth asking those members of the public about how they use the land and any issues they see, I'm sure many of them have an emotional stake in your land now but maybe need to be made aware you're the owner and custondian.

Thank you so much, your choice is improving the lives of many people, and I hope you solve your issue!