Actually, reading the fine print, it was not a 2 hour flight but a 30 minute one (plus transits presumably) flying over central London.
What I find incredible is that you could present yourself at Charles St SW1 at 2.30pm, be driven down to Croydon Airport, fly for 30 minutes plus and be driven back into central London, all by 4.30pm!
Such a shame that 2 guineas was probably a week's wages for my Grandad at the time; no wonder that it took two more generations of my family before we could afford to fly.