Found this on
BAA's website:
National Express Airport No. 700 - Heathrow & Gatwick. Non-stop inter-airport transfer. (Formerly Speedlink)
This service operates between Gatwick and Heathrow airports. There are dedicated points at both South and North Terminal. Tickets and information can be obtained at the bus and coach ticket desk on the Arrivals level of both South and North Terminal. Average journey time between Heathrow and Gatwick is approximately 80 minutes depending on traffic and time of day. Journeys may take longer at peak traffic times. Further information 08705 757 747 or
www.GoByCoach.com.
Go to
www.GoByCoach.com for full schedules and pricing information.