Google is grumpy at me because I'm missing jobLocation.address.addressRegion from the job advertisements I have on my website.

http://schema.org/addressRegion gives one example - "CA". This is an abbreviation for California, an American state, I'm presuming; though it could just as easily be the ISO two-letter abbreviation for "Canada". The documentation is US-centric and vague.

If addressRegion is intended to be a state, province or prefecture, that's helpful for those countries that have them.

The UK doesn't have any "states". It does have counties, but they are mainly historical, and London isn't in a county. Nor, technically, is Bristol or Manchester, for example. There's nothing I can put there.

While the UK doesn't normally add a nation ("England", "Wales", "Scotland", "Northern Ireland") to an address, is this what is expected in this field?

This is a mandatory field for a jobLocation, yet Google's geodata doesn't include a "nation" or a historical county - https://goo.gl/maps/was25WujcuT2 is a visible example of an address in London. Where might I programmatically get the correct data to satisfy Google's requirement for an addressRegion for a UK address?