To take advantage of the best prices you will need to prove you are a leisure traveller, en route to luton airport, so you will need to provide either yr 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 journey from feltham station to the airport.
Going to the airport by train is great, you can sleep, 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 the station to luton airport is that there must be at least two grown ups 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 luton airport.
make sure you leave plenty of time to get to luton airport early enough to eat, shop and so on, so check the times of trains from feltham station before you go. If you have time to kill at luton airport you can always read or play a game again! As you have bought yr train ticket in advance, you don't need to fret about the opening times of feltham station.
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