Vectisman, your point is well made. It's too simplistic to regard LHR as being a hotbed of captains of industry flying to tiger economies, or to regard LGW as a hellhole full of chavs. UK air travel is dominated by leisure travel, and the only airports with a (bare) majority of business pax are LCY and ABZ, I think.
As for the precise percentages, I don't know where GAL gets its numbers from, but the CAA survey methodology at least has the merit of being consistent between airports, and of being established for many years.