Someone said :
The forty foot does not have nude swimming there any more. It's been only very early on Sunday mornings that some older men still swim naked here. For the best part of 20 years now you are obliged to cover up at the forty foot - the rules clearly state that swimming togs must be worn.
The sign says "togs must be worn" but the voluntary group maintaining the site, the Gentlemen's Swimming Club, regularly attends and tends to the place, asking for voluntary contributions for the use of the facility, often early in the morning or in the afternoon.
One could argue that the sign does not apply to the naturist side of the site, which is physically separate from the front end (Queue for "back end" jokes
And yes, they are in charge of the site, and have keys to the towers there, where they can prepare coffee. So they are not one or two old perverts shamefully bathing in the wee hours of God's own day, as you post suggest... http://www.fortyfoot.org/