There is a regular bus service from London Heathrow to Gerrards Cross. Info here.
If you are arriving at London Gatwick, Luton or Stansted we suggest you take train or bus services into central London and then travel to London Marylebone train station. There are regular train services from London Marylebone to Gerrards Cross. For more information, visit Chiltern Railways website.
For bus services to and from London Gatwick, Luton or Stansted into central London click here.
Visiting London – http://www.visitlondon.com/
Visiting Windsor – http://www.windsor.gov.uk/