I didn’t consider steel doubles a recreational configuration but kind folks here have informed me it is common in the UK.
Not just the UK. I think I mentioned above that I've seen it in North Carolina. Maybe some in Florida, too, though double Al 80s are probably more common. Also, with the increasing popularity of tech diving, we have people who are not yet tech certified but are diving steel doubles to prepare themselves.
When I was at one of the FL springs a few weeks ago another diver who was gearing up mentioned he had just witnessed someone in double tanks flailing about at the surface, apparently a bit negatively buoyant, alternately finning get his head above water and gulp some air, and sinking again. The diver who told me this--an instructor--was shaking his head in disbelief (mainly that the flailing diver had entered the water while his buddies were still in the parking lot). Now, for all I know he may have been there that day to practice valve drills, for the very goal of developing the skill of reaching behind his head to fix problems like a valve being off. The real problem was being unskilled AND buddy-less for what I assume was supposed to be a training/practice dive, but to get back on the main topic, there are good reasons to make very sure our air is on before we splash.