The FAA office formerly in the CAA building at Gatwick is now near Heathrow:
Phone Number: (44)181.754.8819
Fax: (44)181.754.8826
Mailing Address: Federal Aviation Administration
London IFO, EA35
Sipson Court, 595 Sipson Road
West Drayton, Middlesex
London, UB7 0JD
England, U.K.