To activate your Nationality flag, click on "Profile" on the Navigation Bar menu, then the "Information" tab. Scroll down a little and you will see the list of countries available. Click on the button next to your choice, then scroll all the way down to the bottom and hit "Save".
You should now have a nice little flag next to your warning bar below your avatar.
For those of you in Tenerife, you can either use the Spanish flag or the Scottish one (same as Tenerife), or if you still identify youself with England/UK, choose as you see fit.
LR.