So I found a few old threads about Heathrow to Gatwick transfers using the national express bus. We fly in to Heathrow on United at 11:15 AM and have a RyanAir flight out of Gatwick at 17:45. It seems like there isn't enough time to even stop to eat in London according to previous posts. (If I'm wrong, please correct me!) My question is, do we need to buy the National Express ticket before we leave? Do they often sell out? Is the price going to be more on the day of? We are traveling very light (one carry on and one backpack each, just 2 of us), so we can be pretty flexible. Thanks!
The bus between Heathrow and Gatwick is direct doesn't go through London. Buy the tickets at the desk. Unless it has change from a couple of years ago, there is no discount. Both times we used it it was crowded but not full.
You would be wise to go directly to Gatwick and not stop in London. Buy your coach tickets when you arrive at Heathrow. There are at least three direct National Express coaches/hour between Heathrow and Gatwick. If the first one is full (not likely), take the next one.
Arriving at Heathrow at 11 am is usually the time you arrive from West Coast. You avoid all London commuter traffic. You have 6 hours, I think you should have comfortably enough time to take the Piccadilly Tube from Heathrow to London, have lunch and a little stroll to wake you up and then get to Gatwick on time. You say you travel light- if you need to drop your bags you can leave them at left luggage at Victoria station. Be sure to note the times when the train to gatwick departs and allow yourself the full (or as close as you can get ) 2.5- 3 hours at gatwick (although I wouldnt panic about it). Advantage of Tube from Heathrow and train from Gatwick is seldom affected by traffic. When you are through immigration/customs at Heathrow you can judge your timing . The worst I can recall is 1 and a half hours. Leaving via Gatwick is more efficient than Heathrow- H always has long security lines I have not flown Ryanair, so dont know if they have any quirks. If you are leaving bags at Victoiria I would buy my tickets to gatwick at that time rather than wait until its time to leave