Oh come on.... I was there a week or so ago when the laptop[1] was started up, configured for UK, I had typed on it on the UK keyboard and had produced the quotes-character from <shift>2 (and probably £ from <shift>3). It was a working UK keyboard, everything was UK personalised.
I just had to go over and look at it because instead of "s it was giving @s (and probably vice-versa, didn't check; but it was also giving #s in the place of £, etc). Went through the entire Time & Language settings, nothing changed, nothing obviously US-Keyboard/language, sole Language Pack is English (United Kingdom), and all the rest of the choices are UK-centric where it seemed necessary. There's even "ENG UK" explicitly in the systray, but it's all US typing (tested in applications, command prompt, Start|Run... given that prior windowses could certainly not synchronise GUI, application and command prompt language settings under certain circumstances).
But I fixed it, eventually. You want to know how? "Time & Language>Typing>Advanced keyboard settings". It was set at "Use language list (recommended)", which should have been suffucient - after all, there's only the one language pack (UK one) even installed according to elsewhere in the Settings hierarchy. But, it turns out that if I change it to the sole other option of "English (United Kingdom) - United Kingdom" then we get our £ back and " in the right place (where it definitely originally was).
Much apart from the godsawful reorganisation of the Settings under the latest version(s?) of Windows (seems like a drive to reduce the 'top level' classifications, by nesting and redirecting further in the 'tree' of selections), it definitely changed without any obvious reason (or indication), or even having US(/generic-international)-keyboard down as being used anywhere. (In-between checking if this was anything to do with it, I also went into "Text Services and Input Languages>Advanced Key Settings" and changed both the Switch Input Language and Switch Keyboard Layout sequences to Not Assigned. The "To English {UK, etc}" was already "(None)", and the only explicit shift possible. The ">Language Bar" is hidden, and "Docked in the taskbar" is greyed out, leaving only "Floating On Desktop", which is of course unselected.)
...so solved. For now. Until some update/restart undoes my probable-kludge. Grrr...
[1] Mentioned, both before and after the fact, over in the Computer Help thread. But, as I've just helped myself, I'm definitely not seeking assistance on this issue. Just venting about it. I really dislike how Windows has been made to look simpler and more intuitive but actually become drastically more complicated and less easy to use, behind the camoflage...