Resigning from committee

Good afternoon,
I joined a small, local walks committee last year. The committee was established before I joined and had held some walks. A few weeks in, I saw that permission had not been obtained from all the landowners to walk their land, small area but that doesn't matter in the eyes of the law.
I exited the group in April by sending a message into the WhatsApp group.
I certainly don't want to be a part of anything that is not legally tight .
I'm now thinking that I'd be best to send a letter outlining my reasons fir leaving and make it clear that I am in no way connected to the group now.
I'm guessing a straight forward letter would suffice?
Kind regards.

If this is an informal, voluntary committee with no specific legal standing then might you be over thinking this? On the other hand I guess that there's no harm in making your decision clear(er?) in a letter to the committee (chair?).

Thank you ...I actually forgot to mention that the group take the public on walks or at least advertise amd facilitate them , it's not just a group of people who walk together ! Sorry, forgot that part . I'm thinking committee liability ...especially as landowners consent hasn't been obtained from all ...Thanks !

Follow the club/committee's procedure for standing down?

There isn't one . No worries, I'll just drop them a line ! Thank you !