A survey carried out during 2007 showed that some 8500 passengers per day use the Watford-Gatwick service, of whom fewer than 30 per cent. were making journeys from one side of Clapham Junction to the other, and fewer than 3 per cent. were making journeys to and from Gatwick airport.
I understand that Southern (the train operator) intend to make an announcement about plans for this service shortly.