The monarch of England is also the Monarch of Australia, Canada and many other countries. Around the portrait they put the title of the Monarch, which up until 1953 said emperor of India and a few other things. So no matter which country the coin belonged to the portrait had the title.
The front says the country. If it says no country then logically it is the UK, because the UK was the power and everyone knew who they were. Doesn't really explain why the country is not written on it no though, hmm. Do we still think we are the world superpower. Well, we have just become the number one cricketing nation on earth (there are at least 10 countries who play cricket out of 193 countries in the world)