Not sure where in the UK you are[1], but there's not that much of it round here. Mind you, there's not that many public (street-side) toilets open, any more. In the old days there used to be quite a lot of public lavatories, all fully open (or at least during business hours/daylight hours/something similar), but for various reasons (general cost of up-keep; vandalism; other anti-social behaviour; possibly a bit of 'deviant behaviour', IYKWIM) they've generally been boarded/bricked up.
There was a small (IIRC, a two-wide urinal - not even sure if there was a 'pot' you could piss in, or otherwise use) men's toilet right outside the main gate to my old Primary school. Built of exactly the same stone as the Victorian-era school itself and the caretaker's house which it directly adjoined. Smelly and dark, I can't say that it didn't provide 'relief'[2] for me, on occasion, when I'd just departed the establishment and was going to walk home, when I was very young and went home along that road[3]. Not surprisingly, by 20-or-so years ago it had been bricked up, and then eventually demolished. As has now the school itself (a fine building, from an external architectural POV, but probably too difficult to keep in repair 'where it doesn't show'), while the caretaker's house still exists, but is currently shuttered up. But I digress. A lot.
Having been all round the UK, I
have seen coin-operated turnstiles. Although the ones that come most immediately to mind were corridor-height ones (a bit like football stadiums had, and like a number of industrial campuses around here have (even ones that are now demolished, but retain their perimeter fencing/gating) except in the latter case with swipe-card access control). I think the only ones I can recall that were 'leapable' are from the likes of Picadilly Circus underground station (or one or other of the 'Circuses', on that system, I forget), but with so many people passing, and possibly attendants in... well, attendance, it would have been about as obvious you were avoiding the price of a visit as it would be that you were fare-dodging on the Tube system itself. (Yeah, some people will have done it, of course, in both cases.)
What I've seen a lot more of (not being a connoisseur of such things, merely visiting such establishments for the usual necessity) is coin-operated
cubicle doors! Mostly, these are in Victorian-era seaside resorts, although whether the facilities themselves were that old or Edwardian or even early (neo-)Elizabethan, I wouldn't care to say, in hindsight. But this particular method means that you don't have to spend a penny in order to 'spend a penny', but for more involved personal business you might have had to deposit 10p or so. (Speaking only of the male facilities, here, I've no idea if females were condemned
always to tender some form of payment.)
Actually, now I come to think of it, two further contemporary examples come to mind. First of all there's "Superloos". Well, they've been around for a couple of decades, and I'm not sure how much they cost, even, but probably 1GBP. There's at least one in my city. Never used it, but seen it being entered and exited by others. But mostly I think people would got to into McD's or BK or a certain "Poulet dans l'Oile Chaud" establishment originating from somewhere below the Mason-Dixon line... Whether or not they'd want/need to get a meal while they were there.
Secondly, there's (much like already introduced from the very start of this thread) the attendant-charging convenience. There's a couple that I know of in some large market towns in picturesque North Yorkshire. But you
don't get rationed for paper, it's there in the stalls, on their walls (probably in those lockable multi-roll-holding dispensers) to take and use as freely as necessary (until/unless it runs out; the chance of which the attendant is doubtless tasked to offset for any reasonable degree of usage in a single 'session'). And probably soft (though probably not 'velvet'-style) 2/4-ply stuff.
But for the likes of everything from small, remote scenic viewpoint carparks in the remoter parts of the Scottish highlands and islands, a functional (not
too unaesthetic) toilet block provided there will generally be free (and rarely locked), while at the other end of the extreme, major out-of-town/edge-of-town shopping centre loos are (in my experience) utterly free to use (and both individually large and collectively numerous, being array across all the various spurs and levels). But maybe that's because I'm not a regular visitor to the areas of the country that have either retained the more ancient physical barriers to deter unpaid-entry, or reimplemented this system anew in new-build facilities...
[1] Wherever it is, it's got a different set of dictionary spellings... [2] Of a purely toiletry nature!
[3] By the time I was 9, 10 or so, I think I'd found I could get home quicker (it was only about half a mile, either way!) by going out a back entrance of the school, over the Primary and nearly-adjoining Secondary school fields and into my estate that way. And when I discovered a slightly quicker way between parallel roads perpendicular to my route of travel that went through a builders' yard where I recall taking surreptitious relief up against a wall when I'd allowed my bladder to start
really complaining after a scant 1/4 mile walk (Maybe I was just too excited to deal with the issue at school, or it was all the movement that made the issue more 'pressing' than I had thought it would be.) And why am I telling you all this?