Following discussions with The College of Policing, Police Scotland and The Police Service for Northern Ireland (PSNI) Guidance for all of these countries has been updated to be appropriate as at January 2019
It is also available via: www.bn.org.uk/policing
I totally agree with the 'no costume' in a sauna philosophy. I have started to use my local council run leisure centre sauna using a towel. They have signs requiring the wearing of swimwear but so far I have not been challenged. I have my answers ready for such a time. The first being the regard to hygiene and the second, the fact that I am wearing a towel is doing the same as a swim costume. If I need to be asked if I am wearing swimwear, then there should be no concern.
More people need to do this and it will become acceptable in the UK as it is in Germany and other European countries.