Thing is, Gatwick has existed as a commercial airport since 1933. Admittedly it now occupies very much more land than it did in 1933. There was originally a racecourse (horses) on the site, the first aerodrome for light aircraft was built alongside it in the late 1920s. I doubt anyone would have bothered with a bus skid pan pre 1933, and after that the airport was already there, gradually expanding as the years went by, eventually absorbing the racecourse in the 1950s.
When London Country buses were split off from London Transport in 1970 and given to the state-owned National Bus Company an overhaul works was set up at Tinsley Green near the airport to replace the LT facilities used previously, but since London Country was split into 4 parts on privatisation, the works only lasted 15 years in bus company use and was sold separately. A vague memory of this very shortlived facility, which as far as I know never had a skid pan, may have given rise to the story.