My local leisure centre has a sign up outside the sauna, which indicates that swimwear must be worn at all times in the sauna, steam room and surrounding area.
The last time I went, as a bit of an experiment,  I wore a pair of swimming trunks but made the sides as narrow as possible and wore a towel in a way that made it look as though I was naked under my towel. No one questioned if I was naked but I thought, if they had asked, my answer would have been, "If you need to ask, then it is not evident."
Another thought which crossed my mind was, I could soak my trunks in cold water and wear them on my head to keep my head cool, which would solve two issues. If I can keep my head cool, I can stay in the sauna longer and I would be upholding the requirement by wearing swimwear!  I would still have a loose towel which I would be sitting on anyway, in the interests of hygiene, as opposed to the 'required' clingy, sweaty, unhygienic swimwear to sit directly on the sauna benches, as everyone else does! Yuk!
My swimwear is my birthday suit anyway. I rarely swim in anything else!
Everyone must know the benefits of sauna without swimwear. It can't possibly work effectively clothed.

Most continental saunas are textile-free for hygiene reasons - Lycra tends to trap body fluids and allow them to be transmitted in both directions.

Most continental saunas are textile-free for hygiene reasons - Lycra tends to trap body fluids and allow them to be transmitted in both directions.

Except sadly in France  🙁 and in most of Southern Europe too...
I once took a French lady-friend of my wife to a sauna in Slovenia (a very Germanic pat of ex-Yugoslavia); she was so eager to go that I assumed that she knew and it did need occur to me that I should warn her beforehand. You should have seen her face when the first thing I did when getting there was to remove my trunks and fit them into one of the tiny pigeon-holes provided. Mind you, a minimum of explanation was all she required, and she went nude within - literally - the next minute, without any fuss.
In Rome do as the Romans do, I suppose. But I supose that the phrase is wrong, as saunas in Rome are definitely - and unfortunately - not "textilfrei"  🙁

I know from my experiences in Germany and Scandanavia and from my friends from those countries that they look on UK sauna dress requirements as rather strange. They say it goes against all the benefits of a naked sauna. And I agree.

I am still using my local leisure centre (costume mandatory according to signs) sauna, using just a towel. I take a larger towel to wrap around me when out of the cabin and a smaller one for inside the cabin. I sit on the larger one and place the smaller one loosely over my lap to cover. I have been going weekly for a couple of months now and have had no negative response. On one occasion, a guy was in wearing shorts and when he went out to shower, he returned to the cabin with just a towel!

so is it a case that almost everyone would be happy being naked if they just gave it a go? if so - how could we do that in the UK????

I often wonder how many people even realise there are naturist swimming/suana sessions in many leisure centres in the UK. I always think that you have to look for naturist activities, they don't really get widely advertised which is a shame.

I am still using my local leisure centre (costume mandatory according to signs) sauna, using just a towel. I take a larger towel to wrap around me when out of the cabin and a smaller one for inside the cabin. I sit on the larger one and place the smaller one loosely over my lap to cover. I have been going weekly for a couple of months now and have had no negative response. On one occasion, a guy was in wearing shorts and when he went out to shower, he returned to the cabin with just a towel!

I cant see why you would think you would get negative responses you are not naked. Try discussing not using the towel with people and see where that gets you. I only use a towel in saunas to allow me to work my way round to not having to use it and be totally naked. No one has ever objected by the time I am naked. When new people come in and I am naked and there are other people in who have accepted it they just accept it as well. There have also been occasions when others have also stripped off, but not often.

I am still using my local leisure centre (costume mandatory according to signs) sauna, using just a towel. I take a larger towel to wrap around me when out of the cabin and a smaller one for inside the cabin. I sit on the larger one and place the smaller one loosely over my lap to cover. I have been going weekly for a couple of months now and have had no negative response. On one occasion, a guy was in wearing shorts and when he went out to shower, he returned to the cabin with just a towel!

I cant see why you would think you would get negative responses you are not naked. Try discussing not using the towel with people and see where that gets you. I only use a towel in saunas to allow me to work my way round to not having to use it and be totally naked. No one has ever objected by the time I am naked. When new people come in and I am naked and there are other people in who have accepted it they just accept it as well. There have also been occasions when others have also stripped off, but not often.

Apart from the 'costume must be worn' signs, there is another notice which illustrates acceptable clothing. By using a towel, loosely on my lap, it is quite evident that I am not wearing swimwear. It's early days yet. I don't want anyone to complain. As I mentioned above, the guy who was wearing shorts, returned with just a towel.  Maybe it will catch on over time. Maybe not.  I'm happy using a towel rather than sitting in a bag of sweat and don't want to push it too much yet.  Baby steps.