What British style guides? The BBC doesn't mention it (and indeed uses it in their style guide). I don't have the full Oxford style guide, but the online version I've found uses singular they. It's obviously not British specifically, but interesting from the perspective of non-native speakers: the EU style guide also recommends using singular they (and again uses it in their style guide). The GDS is obviously pro singular they!

So I'm not sure where you're getting the idea that British style guides do not support this construction.

I don't think there's a particular benefit to using it, other than that it is a very common and suddenly understood form of English, and in many cases easier to understand than an equivalent, but more complex construction. You talk about using it in a formal context, which to a certain extent this is, but more than that it is important for Government websites to be widely understood - if the Government adopts a register that is too far removed from common English, then they will not be as easily understood. Given that there is no apparent confusion with singular they in conventional speech (and given that, in cases where it is ambiguous, it is possible to find alternative sentence constructions), it seems pointless not to use it.

Given the amount of user research that is done on the guidance that is added to the design system, I would imagine they've tested it with users and found it works.

It also fits in with their style guide, which talks about writing in a conversational style, https://www.gov.uk/guidance/content-design/writing-for-gov-u...

That's not a foregone conclusion. It's an active discussion on their github issue.

Yes, their style guide says to use singular "they," and that's what I'm criticizing. Aside from this particular carve-out, it doesn't really align with their style guide, which offers this advise:

* "To keep content understandable, concise and relevant, it should be incisive (friendliness can lead to a lack of precision and unnecessary words)"

* "You should not let caveats dictate unwieldy grammar"

It's perplexing that so many are insisting on creating a problem. There is a perfect solution that affords gender neutrality and incisive language. Why not use it?

Singular they is perfectly reasonable in British English. As others have said it is ancient, and modern. It is more of a purcularity that the singluar they ever became unfashionable.