To take advantage of these prices you will need to prove you are not a business traveller, en route to the airport, so you will need to give either yr flight numbers or yr holiday booking reference. I don't think you will need to provide this when you arrive at the station but you may be asked to provide them on your journey from the station to gatwick airport.
Going to gatwick airport by train is great, you can take a nap, read a book (even at night), play a game, or just stare out of the window... The other restriction to buying these inexpensive train tickets from the station to the airport is that there must be at least two adults travelling together. But another great advantage is that children go free. All children under five go free, and then one kidover five but under sixteen per grown up travelling by train to the airport.
be sure to leave enough time to get to the airport early enough to eat, shop etc, so check the times of trains from the station before you go. If you end up with time to kill at gatwick airport you can always read a book or play travel scrabble again! As you have bought your train ticket in advance, you don't need to fret about the opening times of tattenham-corner station.
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