Single sex groups

There's a fieldwork coming up. The good old field team of Roland, Antony, Tasha and me will be valiantly scouring Norfolk for sediments that hold the information we seek for our interglacial sea level project, however encrypted. And some of us are more equal than others; the plan so far is that Tasha and I go in first and start to do the boring work, under frugal circumstances. When the gentlemen arrive the living standards will be instantly raised. So I'm in the process of booking a spacious lodge for all of us, and have a look at campsites where Tasha and I can reside before that. And while looking at the website of the nearest campsite I got somewhat confused. They claim they don't allow single sex groups! I don't suppose Tasha and I, just being 2, count as a group, so it wouldn't have practical implacations for us. But I was puzzled! I can easily envision single sex groups one might not wish to reside too close to in a very sound-permeable tent; an image of ten-ish 15-year-old males comes to mind. But just suppose the local embroidery club, by sheer coincidence all-female, and even all over 60 and not very rowdy at all, wants to have a nice club outing? Hmm. I'm a bit suprised. Is this even legal? If we get to stay there I'll ask why they have this rule...