To take advantage of the best prices you will need to prove you are a leisure traveller, on the way to the airport, so you will need to provide either yr flight details or yr holiday booking reference. I don't think you will need to give this when you arrive at coventry station but you may be asked to give them on your journey from the station to stansted airport.
Going to the airport by train is great, you can sleep, read a book (even at night), play travel scrabble, or just stare out of the window... The other restriction to buying these cheap 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 16 per adult travelling by train to the airport.
make sure you leave plenty of time to get to stansted airport early enough to eat, shop and so on, so check the times of trains from coventry station before you go. If you end up with time to kill at the airport you can always read a book or play a game again! As you have bought your train ticket in advance, you don't need to worry about the opening times of coventry station.
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