Berwick-upon-Tweed

Now you might we wondering why Berwick should appear in this list, but it has an interesting history. It's been swapped between Scotland and England throughout the years.

The Berwick-upon-Tweed entry on the Wikipedia has the following detail - Since Berwick had changed hands several times, it was traditionally regarded as a special, separate entity, and some proclamations referred to "England, Scotland and the town of Berwick-upon-Tweed". One such was the declaration of the Crimean War against Russia in 1853, which Queen Victoria supposedly signed as "Victoria, Queen of Great Britain, Ireland, Berwick-upon-Tweed and all British Dominions"

Berwick Bridge

the Treaty of Everlasting Peace [between Scotland and England in 1502] stated that Berwick was of England but not in England, so Berwick was always mentioned separately in Acts of Parliament. - read more at www.culture24.org.uk

So I don't count Berwick as a country, but I do claim it as an honourable mention in my travels.