I'll give them the benefit of the doubt and assume that they they use "Britain" as a casual term for the UK, in the same way that people refer to the USA as "America". And yes, the word "country" is not properly used.

I was very surprised by the thrust of the article however; I had assumed that the US was much more violent. Especially given the dearth of firearms in the UK. If this is accurate, it is extraordinarily puzzling, at least to me.

How did the daily mail get this simple fact wrong you ask? Well its the daily mail!