I have to differ with the other fellas on who carries.

I personally carry everywhere I go and know several other people who do the same.
Granted that that is a pretty small number but under Florida law (where I live)

(17) "Securely encased" means in a glove compartment, whether or not locked; snapped in a holster; in a gun case, whether or not locked; in a zippered gun case; or in a closed box or container which requires a lid or cover to be opened for access.

You can carry in a snap holster in the glove compartment, a holster in a shoe box on the seat ect. ect.

I know quite some number of persons who do this but aren't part of the statistics due to the lack of liscensing.

Also there are huge numbers of Floridians with CCW permits, last I saw was around 300,000.
More info on that at http://en.wikipedia.org/wiki/Concealed_carry

If you look at he section " Who Carries?" there are some pretty big numbers for quite a few states, although the data is a little dated it is still representative due to increased demand in recent years.

But to put it into perspective, Fl population is around 16,000,000 with 300,000 permits. 53,000 Sq miles and if 1 out of 6 CCW holders carries that means 1 per square mile for some basic math.
If you figure that all of the people stand on half of the land then it goes to 2 per mile. If someone really cared to do the math it could be a lot more, keeping in mind I was assuming that 1 of 6 permit holders actually wears.

I'll bet thats a hell of a lot more than in the UK.