To take benefit of the best prices you will need to prove you are a leisure traveller, on the way to gatwick airport, so you will need to provide either your flight numbers or your holiday booking reference. I don't think you will need to give this when you arrive at the station but you may be asked to provide them on your travels from the station to the airport.
Going to the airport on the train is great, you can take a nap, read (even at night), play travel scrabble, or just stare out of the window... The other restriction to buying these cheap tickets from edgware station to gatwick airport is that there must be at least two grown ups travelling together. But another great benefit is that children go free. All children under 5 go free, and then one child over 5 but under sixteen per adult travelling on the train to gatwick airport.
be sure to leave plenty of time to get to the airport early enough to eat, shop etc, so check the times of trains from edgware 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 ticket in advance, you don't need to worry about the opening hours of the station.
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