North West
I have done some naked hikes in the Peak District in the past and have a couple of geocaching routes planned that may be possible naked at least in part. There are a couple of routes near the Upper Derwent / Howden reservoirs mentioned in this group and that is indeed where my planned geocaching routes lie.
Whether a route is possible naked can depend on the day you go - weekdays often better than weekends. Even the time of day can make a difference - I once did a circular walk that returned via the Manifold valley and amazingly I was able to do even that bit naked as everyone else had gone home! (See picture)
I don't currently know anyone organising group walks in the Peak District and the chances of you being able to join one of my walks which tend to be weekdays and decided at last minute, are very slim, sorry. I can only encourage you to have a go - plan a walk, the more remote the better*, and hope to do it naked, but enjoy it even if you can't strip off for any of it. Open moorland is good as you can see folk approaching from a long way off (and carry shorts). Best of luck!
*I'm assuming you're ok with map reading / navigation / etc!