The National Express Coach picks up from all terminals at Gatwick and Heathrow Terminal 4 & Heathrow coach station for Terminals 1,2 & 3.
Current Fare: GB�17.50
The journey takes about 70 minutes but allow lots extra in case of traffic jams. There are lots of coaches 7 days a week. Goto the website for more info:
http://www.londontoolkit.com/travel/interairporttransfers_hotelcoach.htm
Alternates are via rail into central London and then out again, or by taxi or hire car - more expensive.