The address is actually on the form (if you have been given the correct one) on page 3:
CAA, PLD
Aviation House
Gatwick Airport South
West Sussex RH6 0YR
Medical:
Medical Division
CAA Safety Regulation Group
Aviation House
Gatwick Airport South
West Sussex RH6 0YR
For enquiries and appointments:
Telephone Call Centre +44 (0)1293 573700
It's all on
www.caa.co.uk
Cheers
Gerard