Interesting points, I know a younger Brit guy who took his equally young wife back to Manchester...and he wasn't that well off!

It'll depend heavily on the visa clerk's assessment of the application. If a visa is granted, and the alien is later identified by the authorities in the UK as an overstayer, that clerk will be blamed to some extent.
The visa is actually an entry visa into the UK, not an exit visa from China. The Chinese passport with the entry visa is what's needed, but immigration at the UK port of entry could still refuse her entry, after a short interview.
I reckon an older Briton with a young Chinese girlfriend needn't apply. No way, Hose!
An older Scottish farmer with a young Filipina wife had his spouse refused a tourist visa for the UK. Yet she was granted a tourist visa for Germany that Christmastime. Happy Christmas to all readers, posters and moderators, by the way!