> It's not quite that simple - you would need to maintain a list of proper >
> nouns and not convert those to lower-case.

True - but you could build a list of those that the converter skips.

> However, my argument is that any British English language file should >
> use sentence case, as that's what is in common use in that language.

Not necessarily true, for example poetry / lyric titles frequently use title
case. For menu settings I'd argue they're titles, and not sentences, eg:

    MP visits India on trade visit (sentence headline).

        vs.

    MP at Home (title headline).

Title case in British English is more formal, more grand - it's a matter of
taste, nor correctness.

--
gl