Gatwick Airport (LGW) : Take the M23 from Gatwick and head towards the M25 Heathrow bound. Take J9 exit and follow the signs to Epsom.
Heathrow Airport (LHR) : Take the M4 and look for M25 turnoff. Follow the signs towards M25 Gatwick bound. Take J9 off the M25 and follow the signs to Epsom.