Some Scouts have been mixed for a long time. In our case, both Cub packs are mixed and have been since they were set up (decades ago).
We have 2 Scout packs, and they are split by gender: 50+ years ago, it was only a boys troupe when it started, then a girls troupe was established about 30-odd years ago and they were eventually allowed to share the Den (as their own troupe within the group), and the Cubs followed that and were mixed from the start, with a second Cub pack being formed due to demand and also being mixed.
The Scouts (we have both Scouts and Venturers together, so 12-18 age range) go on Summer Camp separately (the girls go down as the boys come home to the same place), but camp alongside each other for Easter Camp and do a lot of activities together at other times in the year (and they all help to load the 40' truck to go on summer camp, and do the boat maintenance in winter, etc), while having weekly meetings and other activities completely separate. So everyone knows what to expect going into it.
When I was a Guide, there was an occasional summer camp where the DS or DBro of a Leader came along as well - they were Scouts and they stayed in their own tents with the Leaders tents between theirs and those of the Guides, and parents were informed beforehand. I would be very unhappy as either a Leader (and I was one before I left Guiding at Uni) or a parent if I wasn't informed of DCs who are not born as girls were staying in the same tents as those who were. I don't think I would have a problem if DCs who were born as boys but who are trans and who are transitioning properly were able to join but stayed in their own tents until a complete transition was done (and that those DCs should be actively transitioning, not just saying that they feel they are a girl).
I am not the best at explaining myself, and particularly not in relation to the right words to use, so I hope I have not offended anyone in my clunkiness, but it does seem as though Girl Guiding UK is a bit daft on this one. (TG it is not a legal issue in Ireland yet).