Can't choose United Kingdom as my country

On TA I can choose UK as my country, but on TSA it only lets me choose which region of the UK I am [England] which isn't the country. Any ideas why UK isn't an option over here?

Technically, they're both countries, but yes, it's odd that the list differs from TA and TT.
I never noticed until now as I have England selected on all 3 sites.

There is a difference in the language list too.

Both of the above might be down to the source data and the options available there.