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 provide either yr flight details 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 give them on your journey from stansted-airport station to the airport.
Going to ashford-international airport on the train is great, you can take a nap, read (even at night), play a game, or just gaze out of the window... The other restriction to buying these cheap train tickets from the station to ashford-international airport is that there must be at least two adults travelling together. But another great advantage is that kids go free. All children under 5 go free, and then one child over 5 but under sixteen per adult travelling on the train to ashford-international airport.
make sure you leave enough time to get to ashford-international airport early enough to eat, shop and so on, so check the times of trains from stansted-airport station before you go. If you end up with time to kill at the airport you can always read or play travel scrabble again! As you have bought yr train ticket in advance, you don't need to worry about the opening times of stansted-airport station.
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