I am right now in the process of moving most of my business from the Kingdom of Denmark to the United Kingdom.
During that process I have become a regular customer at the Gatwick Express, the (sometimes) fast train going from London’s second largest airport to central London.
When buying tickets online they require you to enter a billing address. Here you can choose between entering a UK address or an international address.
If you enter a UK address the site takes advantage of the UK postal code system where you just have to enter a postcode, which is very granular in the UK, and a house number, and then the system will know your address.
Alternatively you can choose to enter an international address. In that case you will get a form with more fields for you to enter. But, in order not to be too international the form still have the UK way of formatting an address.
Also the default country is United Kingdom which I guess is the only value that should not be applicable for this form.