To take advantage of the best prices you will need to prove you are a leisure traveller, en route to the airport, so you will need to give either yr flight numbers or your 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 travels from the station to the airport.
Going to the airport on the 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 caveat to buying these cheap tickets from leeds station to gatwick airport is that there must be at least two adults 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 the airport.
be sure to leave plenty of time to get to the airport early enough to eat, shop and so on, so check the times of trains from leeds 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 yr ticket in advance, you don't need to fret about the opening hours of the station.
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