Wow, I actually get it! Using the points scale on the right-hand-side, the final positions in the championship (drivers) for each country are added up. So in 2010, Hamilton and Button (then the top and only 2 British drivers in the field) finished 4th and 5th. So 5 points and 4 points = 9 points.
Here is the chart showing how the nations have progressed through time. Note the obvious - such the points where the lines go up very quickly (Italy/Arg in the 50s, Britain in the 60s, France in the 80s and Germany in the 90s and forever more...!)
Can I just say as well, due to a mistake in the preparation of the spreadsheet (i.e. text format being copied from the row above) the British score should be 499, including the 10 from 1994 and the 6 from 2002.