The situation that people find the most easiest to be naked are taking part in indoor activities where everyone is already naked and there are no non-naked people to see them: swimming, sauna, naked yoga. There are many opportunities for these in the UK. The problem is to come up with an activity that people can join in which makes some sense to do naked if you aren’t going to hire a swimming pool or book a spa.
The situation that most people find the hardest to be naked is in a public place where anyone can see them and they are the only one naked.